/* Bố cục: hero chữ bên trái + thẻ "khung video" bên phải; danh mục video nhóm theo series, mỗi dòng là một video đánh số. */
:root {
  --bg: #EFF6FF; --bg2: #E0F2FE; --panel: #FFFFFF; --edge: #BFDBFE;
  --ink: #0F172A; --muted: #475569;
  --blue: #2563EB; --sky: #0EA5E9; --mint: #06D6A0; --yellow: #FACC15;
  --on: #FFFFFF;
  --grad: linear-gradient(120deg, var(--blue), var(--sky) 55%, var(--mint));
  --f-display: "Be Vietnam Pro", "Inter", system-ui, sans-serif;
  --f-body: "Inter", system-ui, -apple-system, "Segoe UI", sans-serif;
  --f-mono: "JetBrains Mono", ui-monospace, "SFMono-Regular", Menlo, monospace;
  --r: 14px;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0A1322; --bg2: #0E1D33; --panel: #111F36; --edge: #1F3B60;
    --ink: #E5EDF7; --muted: #9AABC2; --blue: #60A5FA; --sky: #38BDF8; --mint: #34D399; --on: #0A1322;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0A1322; --bg2: #0E1D33; --panel: #111F36; --edge: #1F3B60;
  --ink: #E5EDF7; --muted: #9AABC2; --blue: #60A5FA; --sky: #38BDF8; --mint: #34D399; --on: #0A1322;
  color-scheme: dark;
}

* { box-sizing: border-box; }
@media (prefers-reduced-motion: no-preference) { html { scroll-behavior: smooth; } }
body {
  margin: 0; padding-inline: 16px;
  background: linear-gradient(180deg, var(--bg), var(--bg2) 60%, var(--bg));
  background-color: var(--bg);
  color: var(--ink); font: 400 16px/1.6 var(--f-body);
}
img { max-width: 100%; height: auto; }
a { color: var(--blue); }
a:focus-visible, button:focus-visible, input:focus-visible { outline: 3px solid var(--sky); outline-offset: 2px; }
[hidden] { display: none !important; }
.sr { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); }
.muted { color: var(--muted); }

.top, main, .foot { max-width: 1080px; margin-inline: auto; }
.top { display: flex; align-items: center; justify-content: space-between; gap: 16px; padding-block: 18px; flex-wrap: wrap; }
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; color: var(--ink); font: 800 20px/1 var(--f-display); }
.brand img { border-radius: 10px; }
.brand b { background: var(--grad); -webkit-background-clip: text; background-clip: text; color: transparent; }
.top-links { display: flex; gap: 18px; flex-wrap: wrap; }
.top-links a { color: var(--muted); text-decoration: none; font-weight: 500; font-size: 15px; }
.top-links a:hover { color: var(--blue); }

.hero { display: grid; grid-template-columns: minmax(0, 1.25fr) minmax(0, 1fr); gap: 40px; align-items: center; padding-block: 24px 48px; }
.eyebrow { margin: 0 0 12px; font: 500 13px/1.4 var(--f-mono); letter-spacing: .04em; color: var(--blue); text-transform: uppercase; }
h1 { margin: 0; font: 800 clamp(34px, 5.4vw, 58px)/1.14 var(--f-display); letter-spacing: -.02em; text-wrap: balance; }
.hl { background: linear-gradient(transparent 74%, color-mix(in srgb, var(--yellow) 85%, transparent) 74%, color-mix(in srgb, var(--yellow) 85%, transparent) 90%, transparent 90%); padding-inline: 2px; }
.lead { max-width: 60ch; margin: 20px 0 0; font-size: 18px; color: var(--muted); }
.cta { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 28px; }
.btn { display: inline-flex; align-items: center; padding: 12px 20px; border-radius: 999px; font-weight: 600; text-decoration: none;
  color: var(--ink); background: var(--panel); border: 1.5px solid var(--edge); transition: transform .15s, border-color .15s; }
.btn:hover { border-color: var(--blue); transform: translateY(-1px); }
.btn-yt { background: var(--grad); color: var(--on); border-color: transparent; }
.socials { display: flex; flex-wrap: wrap; align-items: center; gap: 6px 16px; margin: 20px 0 0; font: 500 15px/1.4 var(--f-body); }
.socials span { color: rgba(255, 255, 255, .85); }
.socials a { color: #fff; font-weight: 600; text-underline-offset: 4px; text-decoration-color: rgba(255, 255, 255, .5); }
.socials a:hover { color: #FDE047; text-decoration-color: currentColor; }
.stats { margin: 22px 0 0; font: 500 14px/1.4 var(--f-mono); color: var(--muted); font-variant-numeric: tabular-nums; }

/* Dải đầu trang phủ màu logo, Mark và Bit đứng bên phải */
.band { margin-inline: -16px; padding-inline: 16px; color: #fff;
  background: linear-gradient(120deg, #2563EB 0%, #0EA5E9 55%, #06D6A0 100%); }
.band-in { max-width: 1080px; margin-inline: auto; }
.band .brand, .band .top-links a, .band h1, .band .lead, .band .stats, .band .eyebrow { color: #fff; }
.band .top-links a:hover { color: #FDE047; }
.band .brand img { background: #fff; padding: 3px; }
.band .brand b { background: none; color: #FDE047; -webkit-text-fill-color: #FDE047; }
.band .lead { color: rgba(255, 255, 255, .92); }
.band .eyebrow { opacity: .9; }
.band .hl { background: #FACC15; color: #0F172A; padding: 0 10px; border-radius: 10px; -webkit-box-decoration-break: clone; box-decoration-break: clone; }
.band .btn { background: rgba(255, 255, 255, .14); color: #fff; border-color: rgba(255, 255, 255, .6); }
.band .btn:hover { border-color: #fff; }
.band .btn.btn-yt { background: #FACC15; color: #0F172A; border-color: #FACC15; }
.hero-art { margin: 0; width: 100%; justify-self: center; display: grid; justify-items: center; gap: 6px; }
.hero-art img { width: min(100%, 460px); filter: drop-shadow(0 18px 30px rgba(15, 23, 42, .25)); }
.hero-art figcaption { font: 500 14px/1.4 var(--f-body); background: rgba(15, 23, 42, .28); padding: 6px 14px; border-radius: 999px; }
@media (prefers-reduced-motion: no-preference) {
  .hero-art img { animation: bob 4s ease-in-out infinite; }
  @keyframes bob { 0%, 100% { transform: translateY(0); } 50% { transform: translateY(-6px); } }
}

h2 { margin: 0; font: 800 clamp(26px, 3.4vw, 34px)/1.15 var(--f-display); letter-spacing: -.01em; }
.catalog h2 { display: inline-block; background: linear-gradient(transparent 68%, color-mix(in srgb, var(--yellow) 80%, transparent) 68%, color-mix(in srgb, var(--yellow) 80%, transparent) 92%, transparent 92%); padding-inline: 4px; }
.catalog { padding-block: 48px 40px; }
.catalog-head { display: flex; align-items: end; justify-content: space-between; gap: 16px; flex-wrap: wrap; }
.search { flex: 0 1 320px; min-width: 0; }
.search input { width: 100%; font: 400 16px var(--f-body); color: var(--ink); background: var(--panel);
  border: 2px solid color-mix(in srgb, var(--blue) 35%, var(--edge)); border-radius: 999px; padding: 11px 18px; }
.search input:focus { border-color: var(--blue); outline: none; box-shadow: 0 0 0 4px color-mix(in srgb, var(--sky) 25%, transparent); }

.chips { display: flex; gap: 8px; margin: 22px 0 8px; overflow-x: auto; padding-bottom: 8px; scrollbar-width: thin; }
.chip { flex: none; font: 600 14px/1 var(--f-body); padding: 10px 15px; border-radius: 999px; cursor: pointer;
  color: var(--blue); background: var(--panel); border: 1.5px solid color-mix(in srgb, var(--blue) 30%, var(--edge)); }
.chip:hover { border-color: var(--blue); }
.chip[aria-selected="true"] { background: var(--grad); color: #fff; border-color: transparent; }
.chip small { font: 500 12px var(--f-mono); opacity: .75; margin-left: 4px; }

/* Mỗi series là một thẻ: đầu thẻ phủ dải màu logo, bên trong là danh sách video */
.series { margin-top: 28px; background: var(--panel); border-radius: 22px; overflow: hidden;
  border: 1.5px solid var(--edge); box-shadow: 0 18px 40px -30px rgba(37, 99, 235, .55); }
.series-head { display: grid; grid-template-columns: minmax(0, 1fr) auto; gap: 4px 16px; align-items: baseline;
  padding: 20px 24px 18px; color: #fff; background: linear-gradient(120deg, #2563EB, #0EA5E9 60%, #06D6A0); }
.series:nth-of-type(even) .series-head { background: linear-gradient(120deg, #0EA5E9, #06D6A0 70%, #2DD4BF); }
.series-head h3 { margin: 0; font: 800 22px/1.25 var(--f-display); text-wrap: balance; }
.series-range { font: 500 13px var(--f-mono); color: rgba(255, 255, 255, .9); font-variant-numeric: tabular-nums; }
.series-desc { grid-column: 1 / -1; margin: 0; color: rgba(255, 255, 255, .92); max-width: 70ch; }
.tags { grid-column: 1 / -1; display: flex; flex-wrap: wrap; gap: 6px; margin-top: 8px; }
.tags span { font: 500 12px/1 var(--f-mono); padding: 6px 9px; border-radius: 999px; background: rgba(255, 255, 255, .2); border: 1px solid rgba(255, 255, 255, .45); color: #fff; }
.soon { font: 700 12px/1 var(--f-body); padding: 6px 10px; border-radius: 999px; background: var(--yellow); color: #0F172A; margin-left: 10px; vertical-align: 3px; }

.list { list-style: none; margin: 0; padding: 4px 24px 8px; }
.row { display: grid; grid-template-columns: 52px minmax(0, 1fr) auto; gap: 16px; align-items: start; padding: 16px 0; border-bottom: 1px dashed var(--edge); }
.row:last-child { border-bottom: 0; }
.num { display: inline-grid; place-items: center; width: 48px; height: 34px; border-radius: 10px; font: 500 14px/1 var(--f-mono);
  color: var(--blue); background: color-mix(in srgb, var(--sky) 14%, var(--panel)); border: 1.5px solid color-mix(in srgb, var(--blue) 30%, var(--edge)); font-variant-numeric: tabular-nums; }
.row-main { min-width: 0; }
.row-title { margin: 0; font: 600 17px/1.45 var(--f-body); }
.row-part { display: inline-block; font: 600 12px/1 var(--f-mono); color: #0F172A; background: var(--yellow); padding: 5px 8px; border-radius: 6px; margin-right: 8px; vertical-align: 2px; }
.row-desc { margin: 4px 0 0; color: var(--muted); font-size: 15px; max-width: 72ch; }
.row-link { font: 600 14px/1 var(--f-body); white-space: nowrap; text-decoration: none; color: var(--on); background: var(--blue); padding: 9px 14px; border-radius: 999px; }
.row-link:hover { background: var(--sky); }
.row-soon { font: 600 13px/1 var(--f-body); color: var(--muted); white-space: nowrap; padding: 9px 12px; border-radius: 999px; border: 1.5px dashed var(--edge); }
/* Dải "Hôm nay trên kênh": video ra mắt hôm nay (app.js điền, không có thì ẩn) */
.today { margin-top: 20px; padding: 14px 18px; border-radius: var(--r); background: var(--panel); border: 1.5px solid var(--edge);
  border-left: 5px solid var(--mint); display: flex; flex-wrap: wrap; align-items: center; gap: 10px 18px; }
.today[hidden] { display: none; }
.today-head { margin: 0; font: 800 16px/1.3 var(--f-display); color: var(--ink); }
.today-head span { font: 500 13px var(--f-mono); color: var(--muted); margin-left: 6px; }
.today-list { list-style: none; margin: 0; padding: 0; display: flex; flex-wrap: wrap; gap: 8px; min-width: 0; }
.today-list a { display: inline-flex; align-items: center; gap: 10px; max-width: 100%; padding: 4px 14px 4px 4px; border-radius: 12px;
  text-decoration: none; color: var(--ink); font: 600 15px/1.35 var(--f-body); background: var(--bg2); border: 1.5px solid var(--edge); }
.today-list a:hover { border-color: var(--blue); }
.today-list .num { flex: none; width: 44px; height: 30px; }
@media (max-width: 760px) {
  .today { flex-direction: column; align-items: stretch; }
  .today-list { flex-direction: column; }
}
.xem-them { display: block; width: calc(100% - 48px); margin: 0 24px 18px; padding: 12px; border-radius: 14px; cursor: pointer;
  font: 600 15px/1.2 var(--f-body); color: var(--blue); background: color-mix(in srgb, var(--sky) 10%, var(--panel)); border: 1.5px dashed color-mix(in srgb, var(--blue) 35%, var(--edge)); }
.xem-them:hover { border-style: solid; border-color: var(--blue); }
.empty { color: var(--muted); padding-block: 24px; display: flex; align-items: center; gap: 16px; flex-wrap: wrap; }
.empty img { width: 120px; }
.empty p { margin: 0; max-width: 40ch; }

.about { margin-block: 24px 56px; padding: 36px; border-radius: 28px; display: grid; grid-template-columns: 220px minmax(0, 1fr); gap: 32px; align-items: center;
  background: linear-gradient(135deg, color-mix(in srgb, var(--blue) 12%, var(--panel)), color-mix(in srgb, var(--mint) 20%, var(--panel)));
  border: 1.5px solid color-mix(in srgb, var(--mint) 35%, var(--edge)); }
.about-art { width: 220px; }
.about-text { display: grid; gap: 14px; min-width: 0; }
.about h2 { color: var(--ink); }
.about p { margin: 0; max-width: 68ch; color: var(--ink); opacity: .85; font-size: 17px; }
/* Liên hệ hợp tác (app.js điền email từ data/kenh.json) */
.about .contact { opacity: 1; display: flex; flex-wrap: wrap; align-items: center; gap: 10px 14px; margin-top: 4px; }
.btn-mail { background: var(--blue); color: var(--on); border-color: transparent; overflow-wrap: anywhere; }
.btn-mail:hover { background: var(--sky); }

.foot-band { margin-inline: -16px; padding-inline: 16px; color: #fff; background: linear-gradient(120deg, #1D4ED8, #0EA5E9 60%, #06D6A0); }
.foot { display: grid; grid-template-columns: auto minmax(0, 1fr) auto; align-items: center; gap: 8px 24px; padding-block: 32px; }
.foot .brand { color: #fff; }
.foot .brand img { background: #fff; padding: 3px; border-radius: 9px; }
.foot .brand b { background: none; color: #FDE047; -webkit-text-fill-color: #FDE047; }
.foot-line { margin: 0; color: rgba(255, 255, 255, .9); }
.foot-links { display: flex; flex-wrap: wrap; gap: 8px 16px; }
.foot-links a { color: #fff; font-weight: 600; text-decoration: none; }
.foot-links a:hover { color: #FDE047; }
.foot-copy { grid-column: 1 / -1; font: 500 13px var(--f-mono); color: rgba(255, 255, 255, .8); }

/* "Bắt đầu từ đây": bản đồ 7 vùng của kênh và lộ trình 3 bước cho người mới (link trong bio trỏ về #bat-dau) */
.band .top-links a.nav-start { color: #0F172A; background: #FACC15; padding: 6px 12px; border-radius: 999px; font-weight: 700; margin-block: -6px; }
.band .top-links a.nav-start:hover { color: #0F172A; background: #FDE047; }
.start { padding-block: 48px 8px; scroll-margin-top: 12px; }
.start-head { display: grid; grid-template-columns: 150px minmax(0, 1fr); gap: 24px; align-items: center; }
.start-art { width: 150px; }
.start .eyebrow { margin-bottom: 8px; }
.start h2 { display: inline-block; background: linear-gradient(transparent 68%, color-mix(in srgb, var(--yellow) 80%, transparent) 68%, color-mix(in srgb, var(--yellow) 80%, transparent) 92%, transparent 92%); padding-inline: 4px; }
.start-lead { margin: 12px 0 0; max-width: 62ch; font-size: 17px; color: var(--muted); }
.regions { list-style: none; margin: 28px 0 0; padding: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(min(100%, 320px), 1fr)); gap: 16px; }
.region { display: flex; flex-direction: column; gap: 10px; padding: 18px 18px 14px; background: var(--panel); border-radius: 20px;
  border: 1.5px solid var(--edge); border-top: 5px solid var(--sky); box-shadow: 0 18px 40px -30px rgba(37, 99, 235, .55); }
.region:nth-child(3n+1) { border-top-color: var(--blue); }
.region:nth-child(3n) { border-top-color: var(--mint); }
.region-top { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; }
.region-pick { order: 3; font: 700 12px/1 var(--f-body); padding: 6px 10px; border-radius: 999px; background: var(--yellow); color: #0F172A; }
/* Vùng 1 là điểm xuất phát: trải hết chiều ngang, 6 vùng còn lại chia đều */
.region:first-child { grid-column: 1 / -1; }
@media (min-width: 761px) {
  .region:first-child { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 6px 32px; align-items: center; }
  .region:first-child .region-desc { grid-column: 1; }
  .region:first-child .region-list { grid-column: 2; grid-row: 1 / span 2; margin: 0; }
  .region:first-child .region-list li:first-child { border-top: 0; }
}
.region-emoji { flex: none; display: grid; place-items: center; width: 46px; height: 46px; border-radius: 14px; font-size: 24px; line-height: 1;
  background: color-mix(in srgb, var(--sky) 14%, var(--panel)); border: 1.5px solid color-mix(in srgb, var(--blue) 25%, var(--edge)); }
.region-num { font: 500 12px/1 var(--f-mono); color: var(--blue); text-transform: uppercase; letter-spacing: .04em; }
.region h3 { margin: 4px 0 0; font: 800 20px/1.2 var(--f-display); }
.region-desc { margin: 0; color: var(--muted); font-size: 15px; }
.region-list { list-style: none; margin: auto 0 0; padding: 0; }
.region-list li { display: flex; align-items: center; justify-content: space-between; gap: 12px; padding: 10px 0; border-top: 1px dashed var(--edge); }
.region-item { display: grid; gap: 2px; min-width: 0; }
.region-item b { font: 600 15px/1.35 var(--f-body); }
.region-range { font: 500 13px/1.3 var(--f-mono); color: var(--muted); font-variant-numeric: tabular-nums; }
.region-list .row-link, .region-list .row-soon, .step-foot .row-link, .step-foot .row-soon { flex: none; font-size: 13px; }

.path { margin-top: 32px; padding: 28px; border-radius: 28px;
  background: linear-gradient(135deg, color-mix(in srgb, var(--blue) 12%, var(--panel)), color-mix(in srgb, var(--mint) 20%, var(--panel)));
  border: 1.5px solid color-mix(in srgb, var(--mint) 35%, var(--edge)); }
.path h3 { margin: 0; font: 800 clamp(22px, 2.6vw, 26px)/1.2 var(--f-display); }
.path-sub { margin: 8px 0 0; max-width: 64ch; color: var(--ink); opacity: .85; }
.steps { list-style: none; margin: 20px 0 0; padding: 0; display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 16px; counter-reset: none; }
.step { display: flex; gap: 14px; padding: 18px; background: var(--panel); border-radius: 18px; border: 1.5px solid var(--edge); }
.step-num { flex: none; display: grid; place-items: center; width: 40px; height: 40px; border-radius: 50%; font: 800 18px/1 var(--f-display);
  color: #0F172A; background: var(--yellow); border: 2px solid #0F172A; }
.step-main { display: flex; flex-direction: column; gap: 6px; min-width: 0; }
.step-when { margin: 0; font: 500 12px/1.3 var(--f-mono); color: var(--blue); text-transform: uppercase; letter-spacing: .04em; }
.step h4 { margin: 0; font: 800 18px/1.25 var(--f-display); }
.step-desc { margin: 0; color: var(--muted); font-size: 15px; }
.step-foot { margin: auto 0 0; padding-top: 6px; display: flex; flex-direction: column; align-items: flex-start; gap: 8px; }

/* Nút lên đầu trang: hiện khi đã kéo xuống quá phần đầu */
.to-top { position: fixed; right: calc(max(12px, env(safe-area-inset-right, 0px)) + 12px); bottom: calc(100px + env(safe-area-inset-bottom, 0px)); z-index: 20;
  display: inline-flex; align-items: center; justify-content: center; gap: 6px; padding: 11px; border-radius: 999px;
  font: 700 14px/1 var(--f-body); color: #0F172A; background: #FACC15; text-decoration: none;
  border: 2px solid #0F172A; box-shadow: 0 10px 24px -10px rgba(15, 23, 42, .55); transition: transform .15s; }
.to-top span { display: none; }
.to-top:hover { transform: translateY(-2px); }
/* Nút Đầu trang tròn, đứng ngay trên Bit; tạm ẩn khi Bit đang nói hoặc mở menu (bit-tro-ly.js) */
.bit-dang-noi .to-top { visibility: hidden; }
.to-top:focus-visible { outline: 3px solid var(--sky); outline-offset: 3px; }

@media (max-width: 760px) {
  .to-top { padding: 10px; right: calc(max(12px, env(safe-area-inset-right, 0px)) + 7px); bottom: calc(86px + env(safe-area-inset-bottom, 0px)); }
  .hero { grid-template-columns: 1fr; gap: 32px; padding-block: 16px 32px; }
  .hero-art img { width: min(80%, 300px); }
  .about { grid-template-columns: 1fr; padding: 24px; }
  .about-art { width: 170px; }
  .foot { grid-template-columns: 1fr; }
  .list { padding-inline: 16px; }
  .series-head { padding: 18px 16px 16px; grid-template-columns: 1fr; }
  .row { grid-template-columns: 48px minmax(0, 1fr); gap: 12px; }
  .num { width: 44px; }
  .row-link, .row-soon { grid-column: 2; justify-self: start; }
  .top-links { gap: 14px; }
  .start { padding-top: 36px; }
  .start-head { grid-template-columns: 96px minmax(0, 1fr); gap: 14px; align-items: start; }
  .start-art { width: 96px; }
  .path { padding: 20px 16px; }
  .steps { grid-template-columns: 1fr; }
}
@media (min-width: 761px) and (max-width: 980px) {
  .steps { grid-template-columns: 1fr; }
}

/* ===== Trang con: bài viết (bai/*.html), Từ điển AI, bài kiểm tra. Dùng chung dải màu và chân trang với trang chủ ===== */
button.btn { font: inherit; font-weight: 600; cursor: pointer; }
.band .top-links a[aria-current="page"] { color: #FDE047; text-decoration: underline; text-underline-offset: 5px; }
.page-head { padding-block: 4px 40px; }
.page-head h1 { font-size: clamp(30px, 4.4vw, 46px); max-width: 26ch; }
.page-head .lead { font-size: 17px; }
.page-head .cta { margin-top: 22px; align-items: center; }
.crumbs { margin: 0 0 14px; font: 500 13px/1.5 var(--f-mono); color: rgba(255, 255, 255, .85); }
.crumbs a { color: #fff; }
.crumbs a:hover { color: #FDE047; }
.soon-note { font: 600 13px/1 var(--f-body); padding: 8px 12px; border-radius: 999px; background: rgba(15, 23, 42, .28); color: #fff; }
.post-end .soon-note { background: var(--bg2); color: var(--muted); border: 1.5px dashed var(--edge); }
.head-row { display: grid; grid-template-columns: minmax(0, 1fr) auto; gap: 24px; align-items: center; }
.head-art { width: 180px; filter: drop-shadow(0 14px 24px rgba(15, 23, 42, .25)); }

/* Bài viết: cột đọc hẹp, mỗi cảnh của video là một mục */
.doc { max-width: 760px; margin-inline: auto; padding-block: 32px 56px; }
.post { background: var(--panel); border: 1.5px solid var(--edge); border-radius: 22px; padding: 30px 32px; box-shadow: 0 18px 40px -30px rgba(37, 99, 235, .55); }
.post > * + * { margin-top: 26px; }
.post h2 { margin: 0 0 6px; font: 800 22px/1.3 var(--f-display); text-wrap: balance; }
.post p { margin: 0; font-size: 17px; line-height: 1.75; }
.post a { text-underline-offset: 3px; }
.sec-chip { font: 500 12px/1.2 var(--f-mono) !important; color: var(--blue); text-transform: uppercase; letter-spacing: .05em; margin-bottom: 6px !important; }
.try { display: grid; grid-template-columns: 96px minmax(0, 1fr); gap: 18px; align-items: start; padding: 20px 22px; border-radius: 18px;
  background: #FEF9C3; color: #0F172A; border: 2px solid #0F172A; box-shadow: 5px 5px 0 #0F172A; }
.try img { width: 96px; }
.try h2 { color: #0F172A; }
.try a { color: #1D4ED8; }
.try-label { display: inline-block; font: 700 12px/1 var(--f-body) !important; background: #FACC15; color: #0F172A; padding: 6px 10px; border-radius: 999px;
  text-transform: uppercase; letter-spacing: .05em; margin-bottom: 8px !important; border: 1.5px solid #0F172A; }
/* Prompt mẫu trong khung "Thử ngay" + nút chép (bai-viet.js) */
.try .try-prompt { margin-top: 12px; padding: 10px 12px; border-radius: 10px; background: #fff; border: 1.5px dashed #0F172A;
  font: 500 15px/1.6 var(--f-mono); overflow-wrap: anywhere; }
.copy-btn { margin-top: 10px; padding: 9px 16px; font: 600 14px/1 var(--f-body); cursor: pointer; background: #0F172A; color: #fff; border: 2px solid #0F172A; }
.copy-btn:hover { background: #1D4ED8; border-color: #1D4ED8; }
.copy-btn[hidden] { display: none; }
.post-end { border-top: 1px dashed var(--edge); padding-top: 22px; }
.post-end p { color: var(--muted); font-size: 15px; line-height: 1.6; }
.post-end .cta { margin-top: 14px; align-items: center; }
.related { margin-top: 32px; }
.related h2, .series-nav-head { margin: 0; font: 800 20px/1.3 var(--f-display); }
.term-chips { list-style: none; margin: 12px 0 0; padding: 0; display: flex; flex-wrap: wrap; gap: 8px; }
.term-chips a { display: inline-block; font: 500 14px/1 var(--f-mono); padding: 10px 13px; border-radius: 999px; text-decoration: none;
  background: var(--panel); border: 1.5px solid color-mix(in srgb, var(--blue) 30%, var(--edge)); }
.term-chips a:hover { border-color: var(--blue); }
.related-more { margin: 10px 0 0; color: var(--muted); font-size: 15px; }
.series-nav { margin-top: 32px; }
.series-nav-head { font-size: 17px; }
.nav-cards { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 12px; margin-top: 12px; }
.nav-card { display: flex; flex-direction: column; gap: 6px; padding: 16px 18px; border-radius: 16px; text-decoration: none; color: var(--ink);
  background: var(--panel); border: 1.5px solid var(--edge); transition: border-color .15s, transform .15s; }
.nav-card:hover { border-color: var(--blue); transform: translateY(-1px); }
.nav-card.next { grid-column: 2; text-align: right; }
.nav-dir { font: 600 13px/1.3 var(--f-body); color: var(--blue); }
.nav-card b { font: 600 15px/1.45 var(--f-body); }
.next-steps { margin-top: 32px; display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 12px; }
.next-step { display: flex; flex-direction: column; gap: 4px; padding: 18px; border-radius: 18px; text-decoration: none; color: var(--ink);
  background: linear-gradient(135deg, color-mix(in srgb, var(--blue) 12%, var(--panel)), color-mix(in srgb, var(--mint) 20%, var(--panel)));
  border: 1.5px solid color-mix(in srgb, var(--mint) 35%, var(--edge)); }
.next-step b { font: 800 18px/1.3 var(--f-display); }
.next-step span { color: var(--muted); font-size: 15px; }
.next-step:hover { border-color: var(--blue); }

/* Từ điển AI */
.dict { padding-block: 8px 56px; }
.dict-tools { position: sticky; top: 0; z-index: 5; display: flex; align-items: center; gap: 8px 16px; flex-wrap: wrap;
  margin-inline: -16px; padding: 14px 16px; background: color-mix(in srgb, var(--bg) 92%, transparent); backdrop-filter: blur(8px); }
.dict-tools .search { flex: 1 1 320px; max-width: 520px; }
.dict-count { margin: 0; font: 500 14px var(--f-mono); color: var(--muted); font-variant-numeric: tabular-nums; }
.az { display: flex; flex-wrap: wrap; gap: 6px; margin: 6px 0 0; }
.az a { display: grid; place-items: center; min-width: 36px; height: 36px; padding-inline: 6px; border-radius: 10px; text-decoration: none;
  font: 500 15px/1 var(--f-mono); background: var(--panel); border: 1.5px solid color-mix(in srgb, var(--blue) 25%, var(--edge)); }
.az a:hover { border-color: var(--blue); }
.letter { margin-top: 28px; scroll-margin-top: 84px; }
.letter h2 { font-size: 28px; color: var(--blue); }
.terms { list-style: none; margin: 12px 0 0; padding: 0; display: grid; grid-template-columns: repeat(auto-fill, minmax(min(100%, 330px), 1fr)); gap: 12px; }
.term { display: flex; flex-direction: column; gap: 6px; padding: 16px 18px; border-radius: 16px; background: var(--panel); border: 1.5px solid var(--edge); scroll-margin-top: 90px; }
.term:target { border-color: var(--blue); box-shadow: 0 0 0 4px color-mix(in srgb, var(--yellow) 70%, transparent); }
.term h3 { margin: 0; font: 800 19px/1.3 var(--f-display); }
.term-vi { font: 500 14px/1.3 var(--f-body); color: var(--muted); }
.term p { margin: 0; font-size: 15.5px; }
.term-links { margin-top: auto !important; padding-top: 4px; display: flex; flex-direction: column; gap: 4px; font-size: 14px !important; }
.term-main { font-weight: 600; text-underline-offset: 3px; }
.term-more { color: var(--muted); }
.term-more a { margin-left: 6px; font-family: var(--f-mono); }
.pdf-card { margin-top: 40px; display: flex; align-items: center; justify-content: space-between; gap: 16px; flex-wrap: wrap; padding: 22px 24px; border-radius: 22px;
  background: linear-gradient(135deg, color-mix(in srgb, var(--blue) 12%, var(--panel)), color-mix(in srgb, var(--mint) 20%, var(--panel)));
  border: 1.5px solid color-mix(in srgb, var(--mint) 35%, var(--edge)); }
.pdf-card b { display: block; font: 800 20px/1.3 var(--f-display); }
.pdf-card span { display: block; color: var(--muted); margin-top: 4px; }

/* Bài kiểm tra */
.quiz-wrap { max-width: 720px; margin-inline: auto; padding-block: 32px 56px; }
.quiz { background: var(--panel); border: 1.5px solid var(--edge); border-radius: 22px; padding: 24px 26px 28px; box-shadow: 0 18px 40px -30px rgba(37, 99, 235, .55); }
.quiz-top { display: flex; justify-content: space-between; font: 500 13px/1 var(--f-mono); color: var(--muted); font-variant-numeric: tabular-nums; }
.bar { height: 8px; margin: 12px 0 22px; border-radius: 999px; overflow: hidden; background: color-mix(in srgb, var(--sky) 15%, var(--panel)); }
.bar i { display: block; height: 100%; width: 0; background: var(--grad); transition: width .3s; }
.q-num { margin: 0; font: 500 12px/1 var(--f-mono); color: var(--blue); text-transform: uppercase; letter-spacing: .05em; }
.q-text { margin: 8px 0 20px; font: 800 clamp(22px, 3.4vw, 28px)/1.3 var(--f-display); text-wrap: balance; outline: none; }
.q-btns { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 12px; }
.q-btn { font: 700 18px/1 var(--f-body); padding: 18px 12px; border-radius: 16px; cursor: pointer; color: var(--ink); background: var(--panel);
  border: 2px solid color-mix(in srgb, var(--blue) 40%, var(--edge)); transition: border-color .15s, transform .15s; }
.q-btn:hover:not(:disabled) { border-color: var(--blue); transform: translateY(-1px); }
.q-btn:disabled { cursor: default; opacity: .6; }
.q-btn.is-right { opacity: 1; background: #DCFCE7; border-color: #16A34A; color: #14532D; }
.q-btn.is-wrong { opacity: 1; background: #FEE2E2; border-color: #DC2626; color: #7F1D1D; }
.q-fb { margin-top: 18px; padding: 16px 18px; border-radius: 16px; border-left: 6px solid var(--mint); background: color-mix(in srgb, var(--mint) 14%, var(--panel)); }
.q-fb.no { border-left-color: #F97316; background: color-mix(in srgb, #F97316 12%, var(--panel)); }
.q-fb p { margin: 0; }
.q-fb p + p { margin-top: 8px; }
.q-verdict { font-weight: 700; }
.q-more { font-size: 15px; }
.q-next { margin-top: 18px; }
.result { display: grid; grid-template-columns: 130px minmax(0, 1fr); gap: 20px; align-items: center; }
.result img { width: 130px; }
.result p { margin: 0; }
.score { margin: 6px 0 8px; font: 800 40px/1.1 var(--f-display); outline: none; }
.rec-h { margin: 24px 0 8px; font: 800 20px/1.3 var(--f-display); }
.rec { margin: 0; padding-left: 20px; display: grid; gap: 8px; }
.q-actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 24px; }
.share-msg { margin: 12px 0 0; color: var(--muted); font-size: 15px; overflow-wrap: anywhere; }
.share-msg:empty { display: none; }
.quiz-src { margin: 16px 0 0; text-align: center; color: var(--muted); font-size: 14px; }
.quiz-static { padding-left: 20px; display: grid; gap: 10px; }
.quiz-static p { margin: 0; }

/* Trang chủ: tên video dẫn tới bài viết; thẻ kiểm tra, từ điển, PDF trong "Bắt đầu từ đây" */
.row-title a { color: inherit; text-decoration: none; }
.row-title a:hover { color: var(--blue); text-decoration: underline; text-underline-offset: 3px; }
.row-read { display: inline-block; margin-top: 6px; font: 600 14px/1.3 var(--f-body); text-underline-offset: 3px; }
.start-extras { margin-top: 20px; display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 16px; }
.extra { display: flex; flex-direction: column; gap: 6px; padding: 18px; border-radius: 20px; text-decoration: none; color: var(--ink);
  background: var(--panel); border: 1.5px solid var(--edge); border-top: 5px solid var(--yellow); box-shadow: 0 18px 40px -30px rgba(37, 99, 235, .55); transition: border-color .15s, transform .15s; }
.extra:hover { border-color: var(--blue); transform: translateY(-1px); }
.extra b { font: 800 19px/1.25 var(--f-display); }
.extra span { color: var(--muted); font-size: 15px; }
.extra em { margin-top: auto; padding-top: 4px; font: 600 14px/1.3 var(--f-body); font-style: normal; color: var(--blue); }

@media (max-width: 760px) {
  .page-head { padding-bottom: 32px; }
  .head-row { grid-template-columns: minmax(0, 1fr) 84px; gap: 12px; align-items: start; }
  .head-art { width: 84px; margin-top: 28px; }
  .post { padding: 22px 18px; border-radius: 18px; }
  .post p { font-size: 16.5px; }
  .try { grid-template-columns: 1fr; gap: 6px; padding: 18px 16px; box-shadow: 4px 4px 0 #0F172A; }
  .try img { width: 72px; }
  .nav-cards, .next-steps { grid-template-columns: 1fr; }
  .nav-card.next { grid-column: auto; text-align: left; }
  .quiz { padding: 20px 16px 24px; }
  .result { grid-template-columns: 84px minmax(0, 1fr); gap: 14px; }
  .result img { width: 84px; }
  .score { font-size: 32px; }
  .start-extras { grid-template-columns: 1fr; }
  .pdf-card { padding: 20px 16px; }
}
.foot-copy a { color: #fff; }
.foot-copy a:hover { color: #FDE047; }

/* Bit đứng cạnh câu hỏi (tiêu đề bài viết, trang Kiểm tra) */
.h-hoi { display: flex; align-items: center; gap: 10px; }
.h-hoi img { flex: none; width: 40px; height: auto; }
.q-head { display: flex; align-items: flex-start; gap: 14px; }
.q-head .q-bit { flex: none; width: 60px; height: auto; margin-top: 4px; }
.q-fb { display: flex; gap: 12px; align-items: flex-start; }
.q-fb .q-bit { flex: none; width: 44px; height: auto; }
@media (max-width: 480px) { .q-head .q-bit { width: 46px; } }

/* Bit trợ lý: góc phải dưới; nút Đầu trang đứng ngay bên trái Bit */
.bit-tl { position: fixed; right: max(12px, env(safe-area-inset-right, 0px)); bottom: calc(12px + env(safe-area-inset-bottom, 0px)); z-index: 30;
  display: flex; flex-direction: column; align-items: flex-end; gap: 8px; pointer-events: none; }
.bit-tl > * { pointer-events: auto; }
.bit-nut { width: 72px; height: 80px; padding: 0; border: 0; background: none; cursor: pointer; animation: bit-bay 3.2s ease-in-out infinite;
  filter: drop-shadow(0 8px 12px rgba(15, 23, 42, .25)); }
.bit-nut img { width: 64px; height: auto; display: block; margin: 0 auto; }
.bit-nut:focus-visible { outline: 3px solid var(--sky); outline-offset: 2px; border-radius: 16px; }
.bit-nay .bit-nut { animation: bit-nay .7s cubic-bezier(.3, 1.6, .5, 1); }
@keyframes bit-bay { 0%, 100% { transform: translateY(0); } 50% { transform: translateY(-6px); } }
@keyframes bit-nay { 0% { transform: scale(.85); } 60% { transform: scale(1.12) rotate(-6deg); } 100% { transform: scale(1); } }
.bit-noi { position: relative; max-width: min(250px, calc(100vw - 32px)); margin-right: 8px; padding: 12px 34px 12px 14px; border-radius: 16px 16px 4px 16px;
  background: var(--panel); color: var(--ink); border: 2px solid var(--ink); box-shadow: 0 10px 24px -12px rgba(15, 23, 42, .5);
  font: 500 14px/1.45 var(--f-body); cursor: pointer; animation: bit-hien .25s ease-out; }
.bit-noi p { margin: 0; }
.bit-x { position: absolute; top: 4px; right: 4px; width: 28px; height: 28px; border: 0; border-radius: 50%; background: none; color: var(--muted);
  font: 700 18px/1 var(--f-body); cursor: pointer; }
.bit-x:hover { background: var(--bg2); color: var(--ink); }
.bit-menu { width: min(300px, calc(100vw - 24px)); padding: 16px; border-radius: 20px; background: var(--panel); color: var(--ink);
  border: 2px solid var(--ink); box-shadow: 0 18px 40px -16px rgba(15, 23, 42, .55); animation: bit-hien .2s ease-out; }
.bit-chao { margin: 0 0 8px; font: 800 17px/1.3 var(--f-display); }
.bit-menu ul { list-style: none; margin: 0; padding: 0; display: grid; gap: 4px; }
.bit-menu a { display: flex; gap: 10px; align-items: center; padding: 9px 10px; border-radius: 12px; color: var(--ink); text-decoration: none; font: 600 14.5px/1.3 var(--f-body); }
.bit-menu a:hover, .bit-menu a:focus-visible { background: var(--bg2); outline: none; }
.bit-meo { margin-top: 10px; padding: 12px; border-radius: 14px; background: color-mix(in srgb, var(--yellow) 22%, var(--panel)); font-size: 14px; }
.bit-meo b { font: 700 12px/1 var(--f-mono); text-transform: uppercase; letter-spacing: .05em; }
.bit-meo p { margin: 6px 0 8px; line-height: 1.45; }
.bit-meo-khac { border: 0; padding: 0; background: none; color: var(--blue); font: 600 13.5px/1 var(--f-body); cursor: pointer; }
@keyframes bit-hien { from { opacity: 0; transform: translateY(8px) scale(.96); } to { opacity: 1; transform: none; } }
@media (max-width: 480px) { .bit-nut { width: 58px; height: 66px; } .bit-nut img { width: 50px; } }
/* Điện thoại: đang kéo xuống thì Bit lùi vào góc, mờ đi (bit-tro-ly.js) */
.bit-nut { transition: opacity .25s, scale .25s; }
.bit-lui .bit-nut { opacity: .35; scale: .8; translate: 0 8px; }
@media (prefers-reduced-motion: reduce) { .bit-nut, .bit-nay .bit-nut, .bit-noi, .bit-menu { animation: none; } }
@media print { .bit-tl { display: none; } }

/* Nút đổi giao diện sáng/tối trên thanh đầu mọi trang (cai-dat.js) */
.top-tools { display: flex; gap: 8px; align-items: center; }
.top-tools button, .top-tools a { display: inline-flex; align-items: center; gap: 6px; height: 34px; padding: 0 12px; border-radius: 999px;
  border: 1.5px solid rgba(255, 255, 255, .55); background: rgba(255, 255, 255, .14); color: #fff; font: 600 13.5px/1 var(--f-body);
  text-decoration: none; cursor: pointer; }
.top-tools button:hover, .top-tools a:hover { background: rgba(255, 255, 255, .26); }
.top-tools button:focus-visible, .top-tools a:focus-visible { outline: 3px solid #FDE047; outline-offset: 2px; }

/* Bản tiếng Anh (en/): ghi chú "video bằng tiếng Việt" */
.lang-note { font: 500 13.5px/1.4 var(--f-body); color: var(--muted); }
.band .lang-note { color: rgba(255, 255, 255, .88); }
.hero .lang-note { margin: 16px 0 0; }
.catalog-note { margin: 10px 0 0; }

/* Icon Lucide (assets/icons.svg) thay emoji, nét đồng bộ */
.ic { width: 1.15em; height: 1.15em; flex: none; vertical-align: -.2em; }
.btn .ic, .row-link .ic, .top-tools .ic { margin-right: 6px; }
.btn { gap: 0; }
.row-link { display: inline-flex; align-items: center; }
.region-emoji { color: var(--blue); }
.region-emoji .ic { width: 24px; height: 24px; }
.bit-menu a .ic { width: 20px; height: 20px; color: var(--blue); }
.bit-meo b { display: inline-flex; align-items: center; gap: 6px; }
.bit-meo b .ic { width: 16px; height: 16px; }
.bit-x { display: grid; place-items: center; }
.bit-x .ic { width: 16px; height: 16px; }
.top-tools .ic { width: 16px; height: 16px; margin-right: 0; }
.top-tools button, .top-tools a { gap: 6px; }

/* Nút Menu: chỉ hiện trên điện thoại, gom các link trang để đầu trang gọn một hàng (cai-dat.js) */
.nut-menu { display: none !important; }
@media (max-width: 760px) {
  .top { row-gap: 10px; padding-block: 14px; }
  .top-tools { margin-left: auto; }
  .top-tools .nhan { display: none; }
  .top-tools button, .top-tools a { padding: 0 10px; }
  .nut-menu { display: inline-flex !important; }
  .top .top-links { display: none; order: 3; width: 100%; flex-direction: column; gap: 2px; padding: 8px; border-radius: 16px;
    background: rgba(15, 23, 42, .24); }
  .top.mo-menu .top-links { display: flex; }
  .band .top-links a { padding: 11px 12px; border-radius: 10px; font-size: 16px; }
  .band .top-links a:hover { background: rgba(255, 255, 255, .12); }
  .band .top-links a.nav-start { margin: 0 0 4px; align-self: flex-start; }
  .xem-them { width: calc(100% - 32px); margin-inline: 16px; }
}