/* ==========================================================================
   Hỏi Đáp 247 — Hệ thống thiết kế
   Site hỏi đáp giáo dục: ưu tiên khả năng đọc công thức và lời giải
   ========================================================================== */

/* --- 1. Biến thiết kế --------------------------------------------------- */
:root {
  /* Màu chủ đạo — xanh dương tin cậy, quen thuộc với môi trường giáo dục */
  --c-primary: #1d4ed8;
  --c-primary-dark: #1739a8;
  --c-primary-light: #eaf0ff;
  --c-accent: #f59e0b;
  --c-accent-dark: #d97706;

  /* Màu theo cấp học — dùng phân biệt danh mục */
  --c-tieuhoc: #ea580c;
  --c-thcs: #0891b2;
  --c-thpt: #1d4ed8;
  --c-daihoc: #7c3aed;

  /* Hộp nội dung đặc biệt trong lời giải */
  --c-tip: #15803d;
  --c-tip-bg: #eefbf2;
  --c-warn: #b45309;
  --c-warn-bg: #fff8e6;
  --c-formula-bg: #f3f6fd;
  --c-verified: #0d7490;
  --c-verified-bg: #ecfafe;

  /* Trung tính */
  --c-text: #16202e;
  --c-text-soft: #4a5565;
  --c-text-mute: #7b8794;
  --c-border: #e3e8ef;
  --c-border-soft: #eef2f7;
  --c-bg: #ffffff;
  --c-bg-soft: #f6f8fb;
  --c-bg-dark: #121a26;

  --f-sans: "Inter", "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --f-serif: "Charter", "Georgia", serif;
  --f-mono: "SF Mono", "Cascadia Mono", Consolas, monospace;

  --sp-1: 4px;  --sp-2: 8px;  --sp-3: 12px; --sp-4: 16px;
  --sp-5: 24px; --sp-6: 32px; --sp-7: 48px; --sp-8: 64px;

  --r-sm: 5px; --r-md: 9px; --r-lg: 14px; --r-full: 999px;

  --sh-sm: 0 1px 2px rgba(16, 24, 40, 0.06);
  --sh-md: 0 4px 14px rgba(16, 24, 40, 0.09);
  --sh-lg: 0 12px 32px rgba(16, 24, 40, 0.13);

  --w-container: 1240px;
  --h-header: 62px;

  --t-fast: 0.15s ease;
  --t-base: 0.25s ease;
}

/* --- 2. Reset ----------------------------------------------------------- */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  font-family: var(--f-sans);
  font-size: 16px;
  line-height: 1.65;
  color: var(--c-text);
  background: var(--c-bg-soft);
  -webkit-font-smoothing: antialiased;
}

img { max-width: 100%; height: auto; display: block; }
a { color: var(--c-primary); text-decoration: none; transition: color var(--t-fast); }
a:hover { color: var(--c-primary-dark); }
ul, ol { margin: 0; padding: 0; }
li { list-style: none; }
button { font-family: inherit; cursor: pointer; border: none; background: none; }

h1, h2, h3, h4 {
  margin: 0; line-height: 1.3; font-weight: 700;
  color: var(--c-text); letter-spacing: -0.015em;
}
h1 { font-size: clamp(1.6rem, 3.6vw, 2.2rem); }
h2 { font-size: clamp(1.28rem, 2.4vw, 1.55rem); }
h3 { font-size: 1.14rem; }
h4 { font-size: 1rem; }
p { margin: 0 0 var(--sp-4); }

code { font-family: var(--f-mono); font-size: 0.92em; }

:focus-visible {
  outline: 2px solid var(--c-primary);
  outline-offset: 2px;
  border-radius: var(--r-sm);
}

/* --- 3. Tiện ích -------------------------------------------------------- */
.container {
  width: 100%; max-width: var(--w-container);
  margin: 0 auto; padding: 0 var(--sp-4);
}
.sr-only {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}
.text-center { text-align: center; }
.hidden { display: none !important; }

/* --- 4. Header ---------------------------------------------------------- */
.site-header {
  position: sticky; top: 0; z-index: 100;
  background: var(--c-bg);
  border-bottom: 1px solid var(--c-border);
  box-shadow: var(--sh-sm);
}
.header-bar {
  display: flex; align-items: center; gap: var(--sp-4);
  min-height: var(--h-header);
}
.logo {
  display: flex; align-items: center; gap: var(--sp-2);
  font-size: 1.2rem; font-weight: 800; color: var(--c-text);
  letter-spacing: -0.03em; white-space: nowrap; flex-shrink: 0;
}
.logo:hover { color: var(--c-text); }
.logo-mark {
  display: grid; place-items: center;
  width: 34px; height: 34px;
  border-radius: var(--r-md);
  background: linear-gradient(135deg, var(--c-primary), #4f7cf7);
  color: #fff;
}
.logo-mark svg { width: 20px; height: 20px; }
.logo-accent { color: var(--c-primary); font-weight: 800; }

.header-search { position: relative; flex: 1; max-width: 460px; }
.header-search input {
  width: 100%; height: 40px;
  padding: 0 40px 0 var(--sp-4);
  font-size: 0.93rem; font-family: inherit; color: var(--c-text);
  border: 1px solid var(--c-border);
  border-radius: var(--r-full);
  background: var(--c-bg-soft);
  transition: border-color var(--t-fast), background var(--t-fast);
}
.header-search input:focus {
  outline: none; background: var(--c-bg); border-color: var(--c-primary);
}
.header-search button {
  position: absolute; right: 4px; top: 4px;
  width: 32px; height: 32px;
  display: grid; place-items: center;
  border-radius: var(--r-full); color: var(--c-text-soft);
  transition: background var(--t-fast), color var(--t-fast);
}
.header-search button:hover { background: var(--c-primary-light); color: var(--c-primary); }
.header-search svg { width: 17px; height: 17px; }

.header-actions { display: flex; align-items: center; gap: var(--sp-2); margin-left: auto; }
.btn-icon {
  width: 36px; height: 36px;
  display: grid; place-items: center;
  border-radius: var(--r-md); color: var(--c-text-soft);
  transition: background var(--t-fast), color var(--t-fast);
}
.btn-icon:hover { background: var(--c-bg-soft); color: var(--c-primary); }
.btn-icon svg { width: 19px; height: 19px; }
.nav-toggle { display: none; }

.main-nav { border-top: 1px solid var(--c-border-soft); }
.nav-list {
  display: flex; align-items: center; gap: var(--sp-1);
  overflow-x: auto; scrollbar-width: none;
}
.nav-list::-webkit-scrollbar { display: none; }
.nav-list > li { flex-shrink: 0; }
.nav-list a {
  display: block; padding: var(--sp-3);
  font-size: 0.9rem; font-weight: 600; color: var(--c-text-soft);
  white-space: nowrap; border-bottom: 2px solid transparent;
  transition: color var(--t-fast), border-color var(--t-fast);
}
.nav-list a:hover { color: var(--c-primary); }
.nav-list a.is-active { color: var(--c-primary); border-bottom-color: var(--c-primary); }

/* --- 5. Nút ------------------------------------------------------------- */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: var(--sp-2);
  padding: 10px 20px;
  font-size: 0.94rem; font-weight: 600; font-family: inherit; line-height: 1.4;
  border-radius: var(--r-md); border: 1px solid transparent;
  transition: background var(--t-fast), color var(--t-fast),
              border-color var(--t-fast), transform var(--t-fast);
  text-align: center;
}
.btn:active { transform: translateY(1px); }
.btn svg { width: 17px; height: 17px; }
.btn-primary { background: var(--c-primary); color: #fff; }
.btn-primary:hover { background: var(--c-primary-dark); color: #fff; }
.btn-accent { background: var(--c-accent); color: #3a2300; }
.btn-accent:hover { background: var(--c-accent-dark); color: #3a2300; }
.btn-outline { border-color: var(--c-border); color: var(--c-text); background: var(--c-bg); }
.btn-outline:hover { border-color: var(--c-primary); color: var(--c-primary); }
.btn-ghost { color: var(--c-text-soft); }
.btn-ghost:hover { background: var(--c-bg-soft); color: var(--c-primary); }
.btn-block { width: 100%; }
.btn-lg { padding: 14px 28px; font-size: 1rem; }
.btn-sm { padding: 7px 14px; font-size: 0.85rem; }

/* --- 6. Hero ------------------------------------------------------------ */
.hero {
  position: relative; padding: var(--sp-8) 0;
  background: linear-gradient(135deg, #16254a 0%, #1d4ed8 55%, #3b82f6 100%);
  color: #fff; overflow: hidden;
}
.hero::after {
  content: ""; position: absolute; inset: 0;
  background-image:
    radial-gradient(circle at 16% 22%, rgba(255,255,255,0.14), transparent 42%),
    radial-gradient(circle at 84% 78%, rgba(255,255,255,0.10), transparent 46%);
  pointer-events: none;
}
.hero-inner { position: relative; z-index: 1; max-width: 800px; margin: 0 auto; text-align: center; }
.hero h1 { color: #fff; margin-bottom: var(--sp-3); }
.hero-tagline {
  font-size: 1.08rem; color: rgba(255,255,255,0.9); margin-bottom: var(--sp-5);
}
.hero-search { display: flex; gap: var(--sp-2); max-width: 620px; margin: 0 auto var(--sp-5); }
.hero-search input {
  flex: 1; height: 52px; padding: 0 var(--sp-5);
  font-size: 1rem; font-family: inherit;
  border: none; border-radius: var(--r-md); box-shadow: var(--sh-md);
}
.hero-search input:focus { outline: 2px solid var(--c-accent); }

.hero-tags {
  display: flex; flex-wrap: wrap; justify-content: center; align-items: center;
  gap: var(--sp-2); font-size: 0.88rem;
}
.hero-tags span { color: rgba(255,255,255,0.74); }
.hero-tags a {
  padding: 5px 14px; color: #fff;
  background: rgba(255,255,255,0.15);
  border: 1px solid rgba(255,255,255,0.22);
  border-radius: var(--r-full);
  transition: background var(--t-fast);
}
.hero-tags a:hover { background: rgba(255,255,255,0.28); color: #fff; }

/* --- 7. Dải thống kê ---------------------------------------------------- */
.stats-bar {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: var(--sp-4); padding: var(--sp-5);
  margin-top: calc(var(--sp-6) * -1);
  position: relative; z-index: 2;
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg); box-shadow: var(--sh-md);
}
.stat { text-align: center; }
.stat-num {
  display: block; font-size: 1.6rem; font-weight: 800;
  color: var(--c-primary); letter-spacing: -0.03em;
  font-variant-numeric: tabular-nums;
}
.stat-label { font-size: 0.84rem; color: var(--c-text-mute); }

/* --- 8. Dải tin cậy ----------------------------------------------------- */
.trust-bar {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
  gap: var(--sp-4);
}
.trust-item {
  display: flex; gap: var(--sp-3); align-items: flex-start;
  padding: var(--sp-4);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
}
.trust-ico {
  flex-shrink: 0; width: 38px; height: 38px;
  display: grid; place-items: center;
  border-radius: var(--r-md);
  background: var(--c-primary-light); color: var(--c-primary);
}
.trust-ico svg { width: 20px; height: 20px; }
.trust-item h4 { margin-bottom: 2px; font-size: 0.94rem; }
.trust-item p { margin: 0; font-size: 0.84rem; line-height: 1.55; color: var(--c-text-soft); }

/* --- 9. Tiêu đề khối ---------------------------------------------------- */
.section { padding: var(--sp-7) 0; }
.section-head {
  display: flex; align-items: flex-end; justify-content: space-between;
  gap: var(--sp-4); margin-bottom: var(--sp-5);
  padding-bottom: var(--sp-3); border-bottom: 2px solid var(--c-border);
}
.section-head h2 { position: relative; padding-left: var(--sp-3); }
.section-head h2::before {
  content: ""; position: absolute; left: 0; top: 50%;
  transform: translateY(-50%);
  width: 4px; height: 1.15em;
  border-radius: var(--r-full); background: var(--c-primary);
}
.section-sub { font-size: 0.9rem; color: var(--c-text-mute); margin: var(--sp-1) 0 0 var(--sp-3); }
.section-link { font-size: 0.9rem; font-weight: 600; white-space: nowrap; flex-shrink: 0; }

/* --- 10. Thẻ câu hỏi ---------------------------------------------------- */
.q-grid {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: var(--sp-4);
}
.q-card {
  display: flex; flex-direction: column;
  padding: var(--sp-4);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
  transition: transform var(--t-base), box-shadow var(--t-base), border-color var(--t-base);
}
.q-card:hover {
  transform: translateY(-2px); box-shadow: var(--sh-md); border-color: #c5d3ea;
}

/* Nhãn cấp học + môn */
.q-tags {
  display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: var(--sp-3);
}
.chip-grade, .chip-subject, .chip-level {
  display: inline-flex; align-items: center; gap: 4px;
  padding: 3px 10px;
  font-size: 0.75rem; font-weight: 700;
  border-radius: var(--r-full); white-space: nowrap;
}
.chip-grade { background: var(--c-primary-light); color: var(--c-primary); }
.chip-subject { background: var(--c-bg-soft); color: var(--c-text-soft); border: 1px solid var(--c-border); }
.chip-level { background: #fef3e2; color: #9a5b11; }
.chip-level.is-easy { background: var(--c-tip-bg); color: var(--c-tip); }
.chip-level.is-hard { background: #fdeaea; color: #b91c1c; }

/* Nhãn đã kiểm duyệt */
.badge-verified {
  display: inline-flex; align-items: center; gap: 4px;
  padding: 3px 10px;
  font-size: 0.75rem; font-weight: 700;
  color: var(--c-verified); background: var(--c-verified-bg);
  border-radius: var(--r-full); white-space: nowrap;
}
.badge-verified svg { width: 13px; height: 13px; }

.q-title {
  margin-bottom: var(--sp-2);
  font-size: 1.02rem; font-weight: 700; line-height: 1.42;
}
.q-title a { color: var(--c-text); }
.q-title a:hover { color: var(--c-primary); }
.q-excerpt {
  flex: 1; margin-bottom: var(--sp-3);
  font-size: 0.88rem; line-height: 1.6; color: var(--c-text-soft);
  display: -webkit-box; -webkit-line-clamp: 2;
  -webkit-box-orient: vertical; overflow: hidden;
}
.q-meta {
  display: flex; flex-wrap: wrap; align-items: center; gap: var(--sp-3);
  padding-top: var(--sp-3);
  border-top: 1px solid var(--c-border-soft);
  font-size: 0.8rem; color: var(--c-text-mute);
}
.q-meta span { display: inline-flex; align-items: center; gap: 5px; }
.q-meta svg { width: 14px; height: 14px; flex-shrink: 0; }
.q-meta .expert-mini { display: inline-flex; align-items: center; gap: 6px; }
.q-meta .expert-mini img { width: 20px; height: 20px; border-radius: 50%; flex-shrink: 0; }

/* Thẻ câu hỏi dạng hàng */
.q-row {
  display: flex; flex-direction: column; gap: var(--sp-2);
  padding: var(--sp-4);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
  transition: box-shadow var(--t-base), border-color var(--t-base);
}
.q-row:hover { box-shadow: var(--sh-md); border-color: #c5d3ea; }
.q-row .q-title { font-size: 1.08rem; }
.q-list { display: flex; flex-direction: column; gap: var(--sp-3); }

/* Danh sách xếp hạng */
.rank-list { display: flex; flex-direction: column; gap: var(--sp-1); }
.rank-item {
  display: flex; align-items: flex-start; gap: var(--sp-3);
  padding: var(--sp-3); border-radius: var(--r-md);
  transition: background var(--t-fast);
}
.rank-item:hover { background: var(--c-bg-soft); }
.rank-num {
  flex-shrink: 0; width: 26px; height: 26px;
  display: grid; place-items: center;
  font-size: 0.82rem; font-weight: 800; color: var(--c-text-mute);
  background: var(--c-bg-soft); border-radius: var(--r-sm);
}
.rank-item:nth-child(1) .rank-num { background: #fef3c7; color: #92400e; }
.rank-item:nth-child(2) .rank-num { background: #e8edf5; color: #475569; }
.rank-item:nth-child(3) .rank-num { background: #fde8d7; color: #9a3412; }
.rank-title {
  font-size: 0.9rem; font-weight: 600; line-height: 1.5; color: var(--c-text);
  display: -webkit-box; -webkit-line-clamp: 2;
  -webkit-box-orient: vertical; overflow: hidden;
}
.rank-title:hover { color: var(--c-primary); }
.rank-meta { font-size: 0.78rem; color: var(--c-text-mute); margin-top: 2px; }

/* --- 11. Thẻ danh mục -------------------------------------------------- */
.cat-grid {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: var(--sp-4);
}
.cat-card {
  display: flex; flex-direction: column; gap: var(--sp-3);
  padding: var(--sp-5);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
  transition: transform var(--t-base), box-shadow var(--t-base);
}
.cat-card:hover { transform: translateY(-3px); box-shadow: var(--sh-md); }
.cat-icon {
  display: grid; place-items: center;
  width: 46px; height: 46px; border-radius: var(--r-md);
  background: var(--c-primary-light); color: var(--c-primary);
}
.cat-icon svg { width: 24px; height: 24px; }
.cat-card h3 { font-size: 1.02rem; color: var(--c-text); }
.cat-card p {
  margin: 0; font-size: 0.86rem; line-height: 1.55; color: var(--c-text-soft);
  display: -webkit-box; -webkit-line-clamp: 3;
  -webkit-box-orient: vertical; overflow: hidden;
}
.cat-count {
  display: inline-flex; align-items: center; gap: 6px;
  margin-top: auto; font-size: 0.86rem; font-weight: 700; color: var(--c-primary);
  font-variant-numeric: tabular-nums;
}
.cat-count svg { width: 15px; height: 15px; flex-shrink: 0; transition: transform var(--t-fast); }
.cat-card:hover .cat-count svg { transform: translateX(3px); }

.cat-block {
  padding: var(--sp-5);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
}
.cat-block-head {
  display: flex; align-items: center; gap: var(--sp-3);
  padding-bottom: var(--sp-3); margin-bottom: var(--sp-3);
  border-bottom: 1px solid var(--c-border-soft);
}
.cat-block-head h3 { flex: 1; }
.cat-sub-list { display: flex; flex-wrap: wrap; gap: var(--sp-2); }
.cat-sub-list a {
  padding: 5px 13px;
  font-size: 0.86rem; color: var(--c-text-soft);
  background: var(--c-bg-soft); border-radius: var(--r-full);
  transition: background var(--t-fast), color var(--t-fast);
}
.cat-sub-list a:hover { background: var(--c-primary-light); color: var(--c-primary); }
.cat-sub-list a b { font-weight: 600; color: var(--c-text-mute); }

.cat-intent {
  padding: var(--sp-2) var(--sp-3);
  font-size: 0.8rem; line-height: 1.5;
  color: var(--c-text-mute); background: var(--c-bg-soft);
  border-left: 2px solid var(--c-border);
  border-radius: 0 var(--r-sm) var(--r-sm) 0;
}

/* --- 12. Bố cục có sidebar --------------------------------------------- */
.layout {
  display: grid; grid-template-columns: minmax(0, 1fr) 320px;
  gap: var(--sp-6); align-items: start;
  padding: var(--sp-6) 0 var(--sp-8);
}
.layout-main { min-width: 0; }
.layout-side { position: sticky; top: calc(var(--h-header) + var(--sp-4)); }

.widget {
  padding: var(--sp-5); margin-bottom: var(--sp-4);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
}
.widget-title {
  padding-bottom: var(--sp-3); margin-bottom: var(--sp-3);
  font-size: 0.93rem; font-weight: 700;
  text-transform: uppercase; letter-spacing: 0.04em;
  color: var(--c-text); border-bottom: 2px solid var(--c-border);
}
.widget-list { display: flex; flex-direction: column; }
.widget-list li { border-bottom: 1px solid var(--c-border-soft); }
.widget-list li:last-child { border-bottom: none; }
.widget-list a {
  display: flex; justify-content: space-between; gap: var(--sp-2);
  padding: var(--sp-3) 0; font-size: 0.89rem; color: var(--c-text-soft);
}
.widget-list a:hover { color: var(--c-primary); }
.widget-list .count {
  font-size: 0.81rem; color: var(--c-text-mute); flex-shrink: 0;
  font-variant-numeric: tabular-nums;
}

.tag-cloud { display: flex; flex-wrap: wrap; gap: var(--sp-2); }
.tag {
  display: inline-block; padding: 5px 13px;
  font-size: 0.84rem; color: var(--c-text-soft);
  background: var(--c-bg-soft);
  border: 1px solid var(--c-border-soft);
  border-radius: var(--r-full);
  transition: all var(--t-fast);
}
.tag:hover { background: var(--c-primary-light); color: var(--c-primary); border-color: var(--c-primary-light); }
.tag.is-active { background: var(--c-primary); color: #fff; border-color: var(--c-primary); }

/* --- 13. Breadcrumb ---------------------------------------------------- */
.breadcrumb-wrap { background: var(--c-bg); border-bottom: 1px solid var(--c-border); }
.breadcrumb {
  display: flex; flex-wrap: wrap; align-items: center; gap: var(--sp-2);
  padding: var(--sp-3) 0; font-size: 0.85rem; color: var(--c-text-mute);
}
.breadcrumb li { display: flex; align-items: center; gap: var(--sp-2); }
.breadcrumb li:not(:last-child)::after { content: "/"; color: var(--c-border); }
.breadcrumb a { color: var(--c-text-soft); }
.breadcrumb a:hover { color: var(--c-primary); }
.breadcrumb [aria-current] { color: var(--c-text); font-weight: 600; }

/* --- 14. Trang câu hỏi chi tiết ---------------------------------------- */
.answer-layout {
  display: grid; grid-template-columns: minmax(0, 1fr) 320px;
  gap: var(--sp-6); align-items: start;
  padding: var(--sp-6) 0 var(--sp-8);
}
.answer-side { position: sticky; top: calc(var(--h-header) + var(--sp-4)); }

.article {
  padding: var(--sp-6);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
}
.article-header {
  padding-bottom: var(--sp-5); margin-bottom: var(--sp-5);
  border-bottom: 1px solid var(--c-border);
}
.article-header h1 { margin-bottom: var(--sp-3); line-height: 1.24; }

.article-meta {
  display: flex; flex-wrap: wrap; align-items: center; gap: var(--sp-4);
  font-size: 0.87rem; color: var(--c-text-mute);
}
.article-meta span { display: inline-flex; align-items: center; gap: 6px; }
.article-meta svg { width: 15px; height: 15px; }

/* Khối chuyên gia trả lời */
.expert-byline {
  display: flex; align-items: center; gap: var(--sp-3);
  padding: var(--sp-4);
  margin-bottom: var(--sp-5);
  background: var(--c-bg-soft);
  border: 1px solid var(--c-border-soft);
  border-radius: var(--r-md);
}
.expert-byline img {
  width: 48px; height: 48px; border-radius: 50%; flex-shrink: 0;
}
.expert-byline .name { font-size: 0.97rem; font-weight: 700; }
.expert-byline .name a { color: var(--c-text); }
.expert-byline .name a:hover { color: var(--c-primary); }
.expert-byline .role { font-size: 0.84rem; color: var(--c-text-mute); }
.expert-byline .verified-note {
  margin-left: auto; padding: var(--sp-2) var(--sp-3);
  font-size: 0.82rem; line-height: 1.45;
  color: var(--c-verified); background: var(--c-verified-bg);
  border-radius: var(--r-md);
}

/* Nội dung lời giải */
.prose { font-size: 1.02rem; line-height: 1.75; color: var(--c-text); }
.prose > p.lead {
  font-size: 1.1rem; color: var(--c-text-soft);
  padding-left: var(--sp-4);
  border-left: 3px solid var(--c-primary);
}
.prose h2 {
  margin: var(--sp-6) 0 var(--sp-3); font-size: 1.35rem;
  padding-bottom: var(--sp-2); border-bottom: 1px solid var(--c-border-soft);
  scroll-margin-top: calc(var(--h-header) + var(--sp-4));
}
.prose h3 {
  margin: var(--sp-5) 0 var(--sp-2); font-size: 1.12rem;
  scroll-margin-top: calc(var(--h-header) + var(--sp-4));
}
.prose p { margin-bottom: var(--sp-4); }
.prose ul, .prose ol { margin: 0 0 var(--sp-4); padding-left: var(--sp-5); }
.prose ul li { list-style: disc; margin-bottom: var(--sp-2); }
.prose ol li { list-style: decimal; margin-bottom: var(--sp-2); }
.prose li::marker { color: var(--c-primary); }
.prose strong { font-weight: 700; }
.prose em { font-style: italic; }
.prose del { color: var(--c-text-mute); }
.prose a { text-decoration: underline; text-decoration-thickness: 1px; text-underline-offset: 2px; }

/* Code inline — dùng cho công thức ngắn */
.prose code {
  padding: 3px 7px; font-size: 0.93em;
  background: var(--c-formula-bg);
  border: 1px solid #d9e2f5; border-radius: var(--r-sm);
  color: #1e3a8a; font-weight: 600;
}

/* Khối công thức nổi bật */
.prose .formula {
  padding: var(--sp-4) var(--sp-5); margin: var(--sp-4) 0;
  font-family: var(--f-mono); font-size: 1.06rem;
  text-align: center; font-weight: 600; line-height: 1.8;
  color: #1e3a8a; background: var(--c-formula-bg);
  border: 1px solid #d9e2f5; border-radius: var(--r-md);
}

.prose blockquote {
  margin: var(--sp-5) 0; padding: var(--sp-4) var(--sp-5);
  font-size: 0.98rem;
  color: var(--c-text-soft); background: var(--c-bg-soft);
  border-left: 3px solid var(--c-accent);
  border-radius: 0 var(--r-md) var(--r-md) 0;
}
.prose blockquote p:last-child { margin-bottom: 0; }

.prose table {
  width: 100%; margin-bottom: var(--sp-5);
  border-collapse: collapse; font-size: 0.93rem;
}
.prose th, .prose td {
  padding: var(--sp-3); text-align: left;
  border: 1px solid var(--c-border); vertical-align: top;
}
.prose th { background: var(--c-bg-soft); font-weight: 600; }
.prose tbody tr:nth-child(even) { background: #fbfcfe; }

/* Hộp mẹo / cảnh báo trong lời giải */
.prose .tip-box, .prose .warning-box {
  padding: var(--sp-4); margin: var(--sp-5) 0;
  font-size: 0.95rem; line-height: 1.65;
  border-radius: var(--r-md); border-left: 3px solid;
}
.prose .tip-box { background: var(--c-tip-bg); border-color: var(--c-tip); color: #14532d; }
.prose .warning-box { background: var(--c-warn-bg); border-color: var(--c-warn); color: #78350f; }
.prose .tip-box p:last-child, .prose .warning-box p:last-child { margin-bottom: 0; }

/* Các bước trong lời giải */
.prose .steps-inline p {
  padding: var(--sp-3) var(--sp-4); margin-bottom: var(--sp-3);
  background: var(--c-bg-soft); border-radius: var(--r-md);
}

.table-scroll { overflow-x: auto; margin-bottom: var(--sp-5); }
.table-scroll table { margin-bottom: 0; }

/* --- 15. Mục lục ------------------------------------------------------- */
.toc-list { display: flex; flex-direction: column; gap: 2px; }
.toc-list a {
  display: block; padding: 7px var(--sp-3);
  font-size: 0.87rem; line-height: 1.45; color: var(--c-text-soft);
  border-left: 2px solid var(--c-border);
  border-radius: 0 var(--r-sm) var(--r-sm) 0;
  transition: all var(--t-fast);
}
.toc-list a:hover { color: var(--c-primary); background: var(--c-bg-soft); }
.toc-list a.is-active {
  color: var(--c-primary); font-weight: 600;
  border-left-color: var(--c-primary); background: var(--c-primary-light);
}
.toc-list .toc-sub a { padding-left: var(--sp-5); font-size: 0.83rem; }
.article-side .toc-list { max-height: 44vh; overflow-y: auto; scrollbar-width: thin; }

.toc-toggle { display: none; }

.read-progress {
  position: fixed; top: 0; left: 0; z-index: 110;
  height: 3px; width: 0;
  background: linear-gradient(90deg, var(--c-primary), var(--c-accent));
  transition: width 0.1s linear;
}

/* --- 16. Nút hữu ích / phản hồi ---------------------------------------- */
.helpful-box {
  display: flex; flex-wrap: wrap; align-items: center; gap: var(--sp-3);
  padding: var(--sp-4); margin-top: var(--sp-6);
  background: var(--c-bg-soft);
  border: 1px solid var(--c-border); border-radius: var(--r-lg);
}
.helpful-box p { margin: 0; font-size: 0.94rem; font-weight: 600; }
.helpful-box .actions { display: flex; gap: var(--sp-2); margin-left: auto; }

/* --- 17. Hộp thông báo ------------------------------------------------- */
.alert {
  display: flex; gap: var(--sp-3);
  padding: var(--sp-4); margin-bottom: var(--sp-5);
  font-size: 0.9rem; line-height: 1.62;
  border-radius: var(--r-md); border: 1px solid transparent;
}
.alert svg { width: 20px; height: 20px; flex-shrink: 0; margin-top: 1px; }
.alert-info { background: var(--c-verified-bg); border-color: #bfe6f2; color: #0a4f63; }
.alert-warn { background: var(--c-warn-bg); border-color: #fde9b5; color: #78350f; }
.alert-success { background: var(--c-tip-bg); border-color: #b9e6c9; color: #14532d; }
.alert a { font-weight: 600; }

/* --- 18. Công cụ tương tác --------------------------------------------- */
.tool-card {
  padding: var(--sp-6);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
}
.tool-head {
  display: flex; align-items: center; gap: var(--sp-4);
  padding-bottom: var(--sp-4); margin-bottom: var(--sp-5);
  border-bottom: 1px solid var(--c-border);
}
.tool-head .cat-icon { width: 52px; height: 52px; }
.tool-head h2 { margin-bottom: 2px; }
.tool-head p { margin: 0; font-size: 0.9rem; color: var(--c-text-soft); }

.tool-result {
  padding: var(--sp-5); margin-top: var(--sp-5);
  background: linear-gradient(135deg, #f3f7ff, var(--c-primary-light));
  border: 1px solid #cfdcf7; border-radius: var(--r-lg);
}
.tool-result-big {
  font-size: clamp(2rem, 6vw, 3rem); font-weight: 800;
  line-height: 1; color: var(--c-primary);
  letter-spacing: -0.03em; margin-bottom: var(--sp-2);
  font-variant-numeric: tabular-nums;
}
.result-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(110px, 1fr));
  gap: var(--sp-3); margin-top: var(--sp-4);
}
.result-box {
  padding: var(--sp-3); text-align: center;
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-md);
}
.result-box .label {
  font-size: 0.76rem; text-transform: uppercase; letter-spacing: 0.05em;
  color: var(--c-text-mute); margin-bottom: 2px;
}
.result-box .value {
  font-size: 1.3rem; font-weight: 800; color: var(--c-text);
  font-variant-numeric: tabular-nums;
}

/* Bảng điểm nhập liệu */
.score-rows { display: flex; flex-direction: column; gap: var(--sp-3); }
.score-row {
  display: grid; grid-template-columns: 1fr 110px;
  gap: var(--sp-3); align-items: center;
}
.score-row label { font-size: 0.92rem; font-weight: 600; }
.score-row input { text-align: center; }

/* --- 19. Biểu mẫu ------------------------------------------------------ */
.form-grid { display: grid; gap: var(--sp-4); }
.form-grid.cols-2 { grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); }
.field { display: flex; flex-direction: column; gap: 6px; }
.field label { font-size: 0.88rem; font-weight: 600; color: var(--c-text); }
.field label .req { color: #dc2626; }
.field input, .field select, .field textarea {
  padding: 11px var(--sp-4);
  font-size: 0.94rem; font-family: inherit; color: var(--c-text);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-md);
  transition: border-color var(--t-fast), box-shadow var(--t-fast);
}
.field input:focus, .field select:focus, .field textarea:focus {
  outline: none; border-color: var(--c-primary);
  box-shadow: 0 0 0 3px var(--c-primary-light);
}
.field textarea { min-height: 130px; resize: vertical; }
.field-hint { font-size: 0.82rem; color: var(--c-text-mute); }
.check-row {
  display: flex; align-items: flex-start; gap: var(--sp-2);
  font-size: 0.89rem; color: var(--c-text-soft);
}
.check-row input { margin-top: 4px; flex-shrink: 0; }

/* --- 20. Toolbar & phân trang ------------------------------------------ */
.toolbar {
  display: flex; flex-wrap: wrap; align-items: center; gap: var(--sp-3);
  padding: var(--sp-4); margin-bottom: var(--sp-5);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
}
.toolbar-info { font-size: 0.89rem; color: var(--c-text-soft); margin-right: auto; }
.toolbar-info b { color: var(--c-text); font-variant-numeric: tabular-nums; }

.select-wrap { position: relative; }
.select-wrap select {
  appearance: none; height: 38px;
  padding: 0 36px 0 var(--sp-4);
  font-size: 0.87rem; font-family: inherit; font-weight: 500;
  color: var(--c-text); background: var(--c-bg);
  border: 1px solid var(--c-border); border-radius: var(--r-md);
  cursor: pointer;
}
.select-wrap select:focus { outline: none; border-color: var(--c-primary); }
.select-wrap::after {
  content: ""; position: absolute; right: 14px; top: 50%;
  width: 7px; height: 7px; margin-top: -5px;
  border-right: 2px solid var(--c-text-soft);
  border-bottom: 2px solid var(--c-text-soft);
  transform: rotate(45deg); pointer-events: none;
}

.view-toggle {
  display: flex; gap: 2px; padding: 3px;
  background: var(--c-bg-soft); border-radius: var(--r-md);
}
.view-toggle button {
  width: 32px; height: 32px;
  display: grid; place-items: center;
  border-radius: var(--r-sm); color: var(--c-text-mute);
  transition: all var(--t-fast);
}
.view-toggle button svg { width: 16px; height: 16px; }
.view-toggle button.is-active {
  background: var(--c-bg); color: var(--c-primary); box-shadow: var(--sh-sm);
}

.filter-chips { display: flex; flex-wrap: wrap; gap: var(--sp-2); margin-bottom: var(--sp-4); }

.pagination {
  display: flex; flex-wrap: wrap; justify-content: center; align-items: center;
  gap: var(--sp-2); margin-top: var(--sp-6);
}
.pagination a, .pagination span {
  min-width: 40px; height: 40px;
  display: grid; place-items: center;
  padding: 0 var(--sp-3);
  font-size: 0.9rem; font-weight: 600;
  color: var(--c-text-soft); background: var(--c-bg);
  border: 1px solid var(--c-border); border-radius: var(--r-md);
  transition: all var(--t-fast);
  font-variant-numeric: tabular-nums;
}
.pagination a:hover { border-color: var(--c-primary); color: var(--c-primary); }
.pagination .is-active { background: var(--c-primary); border-color: var(--c-primary); color: #fff; }
.pagination .is-disabled { opacity: 0.45; pointer-events: none; }
.pagination .dots { border: none; background: none; }

/* --- 21. Carousel ngang ------------------------------------------------ */
.carousel { position: relative; }
.carousel-track {
  display: flex; gap: var(--sp-4);
  overflow-x: auto;
  scroll-snap-type: x mandatory;
  scroll-behavior: smooth;
  padding: 4px 4px var(--sp-3);
  margin: -4px -4px 0;
  scrollbar-width: none; -ms-overflow-style: none;
}
.carousel-track::-webkit-scrollbar { display: none; }
.carousel-track > * {
  flex: 0 0 calc((100% - var(--sp-4) * 2) / 3);
  scroll-snap-align: start;
}
.carousel-nav { display: flex; gap: var(--sp-2); }
.carousel-btn {
  width: 38px; height: 38px;
  display: grid; place-items: center;
  color: var(--c-text-soft); background: var(--c-bg);
  border: 1px solid var(--c-border); border-radius: var(--r-full);
  transition: all var(--t-fast);
}
.carousel-btn:hover:not(:disabled) {
  border-color: var(--c-primary); color: var(--c-primary);
  background: var(--c-primary-light);
}
.carousel-btn:disabled { opacity: 0.35; cursor: default; }
.carousel-btn svg { width: 18px; height: 18px; }
.carousel-dots { display: flex; justify-content: center; gap: 6px; margin-top: var(--sp-4); }
.carousel-dots button {
  width: 7px; height: 7px; padding: 0;
  border-radius: var(--r-full); background: var(--c-border);
  transition: all var(--t-fast);
}
.carousel-dots button.is-active { width: 22px; background: var(--c-primary); }

/* --- 22. Thẻ chuyên gia ------------------------------------------------ */
.expert-grid {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: var(--sp-4);
}
.expert-card {
  padding: var(--sp-5); text-align: center;
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
  transition: transform var(--t-base), box-shadow var(--t-base);
}
.expert-card:hover { transform: translateY(-3px); box-shadow: var(--sh-md); }
.expert-card img {
  width: 84px; height: 84px; border-radius: 50%;
  margin: 0 auto var(--sp-3);
}
.expert-card h3 { font-size: 1.05rem; margin-bottom: 2px; }
.expert-card .role {
  font-size: 0.86rem; color: var(--c-primary); font-weight: 600;
  margin-bottom: var(--sp-3);
}
.expert-card p { font-size: 0.88rem; line-height: 1.6; color: var(--c-text-soft); }
.expert-card .subjects {
  display: flex; flex-wrap: wrap; gap: 6px; justify-content: center;
  margin-top: var(--sp-3);
}
.expert-stats {
  display: flex; justify-content: center; gap: var(--sp-4);
  margin-top: var(--sp-3); padding-top: var(--sp-3);
  border-top: 1px solid var(--c-border-soft);
  font-size: 0.82rem; color: var(--c-text-mute);
}
.expert-stats b { color: var(--c-text); font-variant-numeric: tabular-nums; }

/* Biến thể 2 cột — thẻ rộng hơn, bố cục ngang, dùng ở trang đội ngũ */
.expert-grid.cols-2 {
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--sp-5);
}
.expert-grid.cols-2 .expert-card {
  display: flex; gap: var(--sp-4);
  text-align: left; align-items: flex-start;
  padding: var(--sp-5);
}
.expert-grid.cols-2 .expert-card img {
  width: 96px; height: 96px; margin: 0; flex-shrink: 0;
}
.expert-grid.cols-2 .expert-card .card-body { flex: 1; min-width: 0; }
.expert-grid.cols-2 .expert-card h3 { font-size: 1.16rem; }
.expert-grid.cols-2 .expert-card .role { font-size: 0.9rem; margin-bottom: var(--sp-2); }
.expert-grid.cols-2 .expert-card p { font-size: 0.91rem; }
.expert-grid.cols-2 .expert-card .subjects { justify-content: flex-start; }
.expert-grid.cols-2 .expert-stats { justify-content: flex-start; }

/* --- 23. Trạng thái rỗng ----------------------------------------------- */
.empty-state {
  padding: var(--sp-8) var(--sp-5); text-align: center;
  background: var(--c-bg); border: 1px dashed var(--c-border);
  border-radius: var(--r-lg);
}
.empty-state svg { width: 54px; height: 54px; margin: 0 auto var(--sp-4); color: var(--c-border); }
.empty-state h3 { margin-bottom: var(--sp-2); }
.empty-state p { color: var(--c-text-soft); max-width: 440px; margin: 0 auto var(--sp-4); }

/* --- 24. Gợi ý tìm kiếm ------------------------------------------------ */
.search-suggest {
  position: absolute; top: calc(100% + 6px); left: 0; right: 0; z-index: 60;
  max-height: 400px; overflow-y: auto;
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-md); box-shadow: var(--sh-lg);
}
.search-suggest:empty { display: none; }
.suggest-item {
  display: block; padding: var(--sp-3) var(--sp-4);
  border-bottom: 1px solid var(--c-border-soft);
}
.suggest-item:last-child { border-bottom: none; }
.suggest-item:hover { background: var(--c-bg-soft); }
.suggest-title { font-size: 0.88rem; font-weight: 600; color: var(--c-text); line-height: 1.42; }
.suggest-meta { font-size: 0.78rem; color: var(--c-text-mute); margin-top: 2px; }

/* --- 25. Bản tin ------------------------------------------------------- */
.newsletter {
  padding: var(--sp-6);
  background: linear-gradient(135deg, #16254a, #1d4ed8);
  border-radius: var(--r-lg); color: #fff; text-align: center;
}
.newsletter h3 { color: #fff; font-size: 1.4rem; margin-bottom: var(--sp-2); }
.newsletter p { color: rgba(255,255,255,0.87); max-width: 540px; margin: 0 auto var(--sp-5); }
.newsletter-form { display: flex; gap: var(--sp-2); max-width: 460px; margin: 0 auto; }
.newsletter-form input {
  flex: 1; height: 46px; padding: 0 var(--sp-4);
  font-size: 0.95rem; font-family: inherit;
  border: none; border-radius: var(--r-md);
}
.newsletter-form input:focus { outline: 2px solid var(--c-accent); }
.newsletter-note { margin: var(--sp-3) 0 0; font-size: 0.82rem; color: rgba(255,255,255,0.7); }

.widget-newsletter {
  background: linear-gradient(135deg, #f3f7ff, var(--c-primary-light));
  border-color: #cfdcf7;
}
.widget-newsletter .widget-title { border-color: #cfdcf7; }

/* --- 26. Trang tĩnh ---------------------------------------------------- */
.page-hero {
  padding: var(--sp-7) 0;
  background: linear-gradient(135deg, #16254a, #1d4ed8);
  color: #fff; text-align: center;
}
.page-hero h1 { color: #fff; margin-bottom: var(--sp-2); }
.page-hero p { max-width: 680px; margin: 0 auto; color: rgba(255,255,255,0.87); }

.doc-page {
  padding: var(--sp-6);
  background: var(--c-bg); border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
}
.doc-page-meta {
  display: flex; flex-wrap: wrap; gap: var(--sp-4);
  padding-bottom: var(--sp-4); margin-bottom: var(--sp-5);
  font-size: 0.86rem; color: var(--c-text-mute);
  border-bottom: 1px solid var(--c-border);
}

.steps { counter-reset: step; display: flex; flex-direction: column; gap: var(--sp-4); }
.step {
  display: flex; gap: var(--sp-4); padding: var(--sp-4);
  background: var(--c-bg-soft); border-radius: var(--r-md);
}
.step::before {
  counter-increment: step; content: counter(step);
  flex-shrink: 0; width: 32px; height: 32px;
  display: grid; place-items: center;
  font-weight: 800; color: #fff; background: var(--c-primary);
  border-radius: var(--r-full);
}
.step h4 { margin-bottom: var(--sp-1); }
.step p { margin: 0; font-size: 0.92rem; color: var(--c-text-soft); }

/* FAQ */
.faq-section {
  padding: var(--sp-5); margin-top: var(--sp-6);
  background: var(--c-bg-soft);
  border: 1px solid var(--c-border); border-radius: var(--r-lg);
}
.faq-item { border-bottom: 1px solid var(--c-border); }
.faq-item:last-child { border-bottom: none; }
.faq-q {
  display: flex; justify-content: space-between; align-items: center; gap: var(--sp-3);
  width: 100%; padding: var(--sp-4) 0;
  font-size: 1rem; font-weight: 600; text-align: left; color: var(--c-text);
}
.faq-q:hover { color: var(--c-primary); }
.faq-q .faq-icon {
  flex-shrink: 0; width: 22px; height: 22px;
  display: grid; place-items: center; color: var(--c-primary);
  transition: transform var(--t-base);
}
.faq-item.is-open .faq-icon { transform: rotate(45deg); }
.faq-a {
  display: none; padding: 0 0 var(--sp-4);
  color: var(--c-text-soft); line-height: 1.7; font-size: 0.95rem;
}
.faq-item.is-open .faq-a { display: block; }

/* --- 27. Footer -------------------------------------------------------- */
.disclaimer-bar {
  padding: var(--sp-3) 0;
  font-size: 0.84rem; line-height: 1.6;
  color: #78350f; background: var(--c-warn-bg);
  border-top: 1px solid #fde9b5; border-bottom: 1px solid #fde9b5;
}
.site-footer {
  padding: var(--sp-7) 0 var(--sp-5);
  background: var(--c-bg-dark); color: #a7b2c2; font-size: 0.89rem;
}
.footer-grid {
  display: grid; grid-template-columns: 1.7fr repeat(3, 1fr);
  gap: var(--sp-6); padding-bottom: var(--sp-6);
  border-bottom: 1px solid rgba(255,255,255,0.1);
}
.footer-brand .logo { color: #fff; margin-bottom: var(--sp-3); }
.footer-brand .logo-accent { color: #7aa2ff; }
.footer-about { line-height: 1.7; margin-bottom: var(--sp-4); }
.footer-contact { display: flex; flex-direction: column; gap: var(--sp-2); font-size: 0.87rem; }
.footer-contact a { color: #a7b2c2; }
.footer-contact a:hover { color: #fff; }
.footer-col h4 {
  margin-bottom: var(--sp-4);
  font-size: 0.86rem; font-weight: 700;
  text-transform: uppercase; letter-spacing: 0.06em; color: #fff;
}
.footer-col li { margin-bottom: var(--sp-2); }
.footer-col a { color: #a7b2c2; }
.footer-col a:hover { color: #fff; }
.footer-social { display: flex; gap: var(--sp-2); margin-top: var(--sp-4); }
.footer-social a {
  width: 36px; height: 36px;
  display: grid; place-items: center; color: #a7b2c2;
  background: rgba(255,255,255,0.08); border-radius: var(--r-md);
  transition: all var(--t-fast);
}
.footer-social a:hover { background: var(--c-primary); color: #fff; }
.footer-social svg { width: 18px; height: 18px; }
.footer-bottom {
  display: flex; flex-wrap: wrap; justify-content: space-between; align-items: center;
  gap: var(--sp-3); padding-top: var(--sp-5);
  font-size: 0.84rem; color: #7d8899;
}
.footer-bottom a { color: #a7b2c2; }
.footer-bottom a:hover { color: #fff; }
.footer-legal { display: flex; flex-wrap: wrap; gap: var(--sp-4); }

.to-top {
  position: fixed; right: var(--sp-5); bottom: var(--sp-5); z-index: 90;
  width: 44px; height: 44px;
  display: grid; place-items: center;
  color: #fff; background: var(--c-primary);
  border-radius: var(--r-full); box-shadow: var(--sh-lg);
  opacity: 0; visibility: hidden; transform: translateY(12px);
  transition: all var(--t-base);
}
.to-top.is-visible { opacity: 1; visibility: visible; transform: translateY(0); }
.to-top:hover { background: var(--c-primary-dark); }
.to-top svg { width: 20px; height: 20px; }

/* --- 28. Responsive ---------------------------------------------------- */
@media (max-width: 1080px) {
  .layout, .answer-layout { grid-template-columns: 1fr; }
  .layout-side, .answer-side { position: static; }
  .footer-grid { grid-template-columns: 1fr 1fr; gap: var(--sp-5); }

  /* Mục lục thành khối gập/mở trên tablet */
  .answer-side .widget-toc { order: -1; }
  .answer-side .toc-list { max-height: none; }
  .toc-toggle {
    display: flex; align-items: center; justify-content: space-between;
    width: 100%; gap: var(--sp-3);
    font-size: 0.93rem; font-weight: 700; font-family: inherit;
    text-transform: uppercase; letter-spacing: 0.04em;
    color: var(--c-text); text-align: left;
    padding-bottom: var(--sp-3); margin-bottom: var(--sp-3);
    border-bottom: 2px solid var(--c-border);
  }
  .toc-toggle .toc-chevron { transition: transform var(--t-base); flex-shrink: 0; }
  .toc-toggle[aria-expanded="false"] .toc-chevron { transform: rotate(-90deg); }
  .toc-toggle[aria-expanded="false"] + .toc-list { display: none; }
  .widget-toc .widget-title { display: none; }
}

@media (max-width: 920px) {
  .carousel-track > * { flex-basis: calc((100% - var(--sp-4)) / 2); }
  /* Thẻ chuyên gia 2 cột -> 1 cột, giữ bố cục ngang cho đỡ cao */
  .expert-grid.cols-2 { grid-template-columns: 1fr; }
}

@media (max-width: 860px) {
  .header-search { display: none; }
  .header-search.is-open {
    display: block; position: absolute; top: 100%; left: 0; right: 0;
    max-width: none; padding: var(--sp-3) var(--sp-4);
    background: var(--c-bg); border-bottom: 1px solid var(--c-border);
  }
  .nav-toggle { display: grid; }
  .main-nav {
    display: none; position: absolute; top: 100%; left: 0; right: 0;
    max-height: 70vh; overflow-y: auto;
    background: var(--c-bg); border-bottom: 1px solid var(--c-border);
    box-shadow: var(--sh-md);
  }
  .main-nav.is-open { display: block; }
  .nav-list { flex-direction: column; align-items: stretch; gap: 0; overflow: visible; }
  .nav-list a { padding: var(--sp-3) var(--sp-4); border-bottom: 1px solid var(--c-border-soft); }
  .nav-list a.is-active { border-bottom-color: var(--c-border-soft); background: var(--c-primary-light); }

  .article, .doc-page, .tool-card { padding: var(--sp-5) var(--sp-4); }
  .expert-byline { flex-wrap: wrap; }
  .expert-byline .verified-note { margin-left: 0; width: 100%; }
  .helpful-box .actions { margin-left: 0; width: 100%; }
}

@media (max-width: 640px) {
  body { font-size: 15.5px; }
  .hero { padding: var(--sp-6) 0; }
  .hero-search { flex-direction: column; }
  .hero-search .btn { width: 100%; }
  .stats-bar { grid-template-columns: repeat(2, 1fr); padding: var(--sp-4); }
  .trust-bar { grid-template-columns: 1fr; }
  .section { padding: var(--sp-6) 0; }
  .section-head { flex-direction: column; align-items: flex-start; gap: var(--sp-2); }
  .q-grid, .cat-grid, .expert-grid { grid-template-columns: 1fr; }
  /* Trên mobile, thẻ chuyên gia quay về bố cục dọc cho dễ đọc */
  .expert-grid.cols-2 .expert-card { flex-direction: column; text-align: center; }
  .expert-grid.cols-2 .expert-card img { margin: 0 auto var(--sp-3); }
  .expert-grid.cols-2 .expert-card .subjects,
  .expert-grid.cols-2 .expert-stats { justify-content: center; }
  .footer-grid { grid-template-columns: 1fr; }
  .footer-bottom { flex-direction: column; align-items: flex-start; }
  .newsletter { padding: var(--sp-5) var(--sp-4); }
  .newsletter-form { flex-direction: column; }
  .carousel-track > * { flex-basis: 100%; }
  .carousel-nav { display: none; }
  .prose { font-size: 0.98rem; }
  .prose .formula { font-size: 0.95rem; padding: var(--sp-3); }
  .score-row { grid-template-columns: 1fr; gap: 4px; }
}

/* --- 29. Chế độ in ----------------------------------------------------- */
@media print {
  .site-header, .site-footer, .layout-side, .answer-side,
  .to-top, .newsletter, .disclaimer-bar, .breadcrumb-wrap,
  .read-progress, .toolbar, .pagination, .helpful-box { display: none !important; }
  body { background: #fff; font-size: 11.5pt; }
  .layout, .answer-layout { display: block; padding: 0; }
  .article, .doc-page { border: none; padding: 0; }
  a { color: var(--c-text); text-decoration: underline; }
  .faq-item .faq-a { display: block !important; }
  .prose table, .prose .formula { page-break-inside: avoid; }
}

/* --- 30. Giảm chuyển động --------------------------------------------- */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}