/* Học Tiếng Trung Giao Tiếp — một cột đọc trên điện thoại, mở rộng 2–3 cột trên máy tính */
:root {
  --bg: #FBF8F4;
  --surface: #FFFFFF;
  --ink: #24201D;
  --muted: #6E6660;
  --line: #E7DFD6;
  --red: #A8201A;
  --red-soft: #F8E9E5;
  --gold: #A97A22;
  --gold-soft: #FBF2DF;
  --good: #2E6A3D;
  --good-soft: #E8F2EA;
  --bad: #A23B2E;
  --on-red: #FFFFFF;
  --font-body: "Be Vietnam Pro", "Helvetica Neue", Arial, sans-serif;
  --font-han: "Noto Serif SC", "Songti SC", serif;
  --wrap: 1080px;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #171413; --surface: #221E1C; --ink: #F1ECE7; --muted: #A9A099; --line: #3A3330;
    --red: #E2564C; --red-soft: #3A201D; --gold: #D9AE5B; --gold-soft: #33291A;
    --good: #7CC48E; --good-soft: #1E2D22; --bad: #EE8A7C; --on-red: #1A0F0E; color-scheme: dark;
  }
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; }
body { margin: 0; background: var(--bg); color: var(--ink); font-family: var(--font-body); font-size: 17px; line-height: 1.6; }
img { max-width: 100%; height: auto; }
a { color: var(--red); }
h1, h2, h3 { line-height: 1.22; margin: 0; text-wrap: balance; }
h2 { font-size: clamp(1.5rem, 3.6vw, 2.1rem); font-weight: 800; margin-bottom: 12px; }
h3 { font-size: 1.1rem; font-weight: 700; margin-bottom: 6px; }
p { margin: 0 0 12px; }
[hidden] { display: none !important; }
:focus-visible { outline: 3px solid var(--gold); outline-offset: 2px; }
.wrap { max-width: var(--wrap); margin: 0 auto; padding-left: max(16px, env(safe-area-inset-left, 0px)); padding-right: max(16px, env(safe-area-inset-right, 0px)); }
.eyebrow { font-size: .78rem; font-weight: 700; letter-spacing: .14em; text-transform: uppercase; color: var(--gold); margin-bottom: 8px; }
.muted { color: var(--muted); }
.small { font-size: .88rem; }
.lead { font-size: 1.12rem; max-width: 40em; }
.num { font-variant-numeric: tabular-nums; }
section { padding-block: 56px 8px; }

/* header */
.top { position: sticky; top: 0; z-index: 30; background: var(--surface); border-bottom: 1px solid var(--line); }
.top .wrap { display: flex; align-items: center; justify-content: space-between; gap: 16px; height: 60px; }
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; color: var(--ink); font-weight: 800; }
.brand .mark { width: 34px; height: 34px; border-radius: 8px; background: var(--red); color: var(--on-red); display: grid; place-items: center; font-family: var(--font-han); font-size: 19px; }
.brand span { font-size: .98rem; }
.nav { display: flex; gap: 20px; align-items: center; }
.nav a { color: var(--ink); text-decoration: none; font-weight: 600; font-size: .95rem; }
.nav .btn { padding: 9px 16px; white-space: nowrap; }
.brand { min-width: 0; }
.brand span:last-child { white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
@media (max-width: 760px) { .nav a:not(.btn) { display: none; } .brand span { font-size: .9rem; } }

.btn { display: inline-flex; align-items: center; justify-content: center; gap: 8px; border: 0; border-radius: 12px; padding: 14px 22px; background: var(--red); color: var(--on-red); font: inherit; font-weight: 700; text-decoration: none; cursor: pointer; }
.btn.ghost { background: transparent; color: var(--red); border: 1.5px solid var(--red); }
.btn.block { width: 100%; }

/* hero */
.hero { background: var(--red); color: var(--on-red); padding-block: 56px 48px; position: relative; overflow: hidden; }
.hero .han { position: absolute; right: max(12px, env(safe-area-inset-right, 0px)); top: 10px; font-family: var(--font-han); font-size: clamp(90px, 22vw, 220px); opacity: .12; line-height: 1; pointer-events: none; }
.hero .eyebrow { color: inherit; opacity: .85; }
.hero h1 { font-size: clamp(2rem, 5.6vw, 3.2rem); font-weight: 800; max-width: 15em; margin-bottom: 14px; }
.hero p { max-width: 36em; opacity: .94; font-size: 1.08rem; }
.hero .actions { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 22px; }
.hero .btn { background: var(--on-red); color: var(--red); }
.hero .btn.ghost { background: transparent; color: var(--on-red); border-color: currentColor; }
.ticks { display: flex; flex-wrap: wrap; gap: 8px 22px; margin-top: 26px; padding: 0; list-style: none; font-weight: 600; font-size: .95rem; }
.ticks li::before { content: "✓ "; }

.grid { display: grid; gap: 14px; }
.g2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.g3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.g4 { grid-template-columns: repeat(4, minmax(0, 1fr)); }
@media (max-width: 860px) { .g3, .g4 { grid-template-columns: repeat(2, minmax(0, 1fr)); } }
@media (max-width: 560px) { .g2, .g3, .g4 { grid-template-columns: 1fr; } }
.card { background: var(--surface); border: 1px solid var(--line); border-radius: 16px; padding: 20px; min-width: 0; }
.card.hl { border: 2px solid var(--red); }
.card.gold { background: var(--gold-soft); border-color: transparent; }
.card ul { margin: 6px 0 0; padding-left: 18px; }
.card li { margin-bottom: 4px; }
.tag { display: inline-block; font-size: .72rem; font-weight: 700; padding: 2px 10px; border-radius: 99px; background: var(--red); color: var(--on-red); margin-bottom: 10px; }
.tag.gold { background: var(--gold); }
.price { font-size: 1.7rem; font-weight: 800; color: var(--red); font-variant-numeric: tabular-nums; line-height: 1.1; }

.stage .n { font-size: 2.2rem; font-weight: 800; color: var(--red); line-height: 1; }
.stage .lvl { font-weight: 700; color: var(--gold); margin: 4px 0 8px; }

.callout { background: var(--gold-soft); border-radius: 14px; padding: 16px 18px; margin: 16px 0; }
.callout.red { background: var(--red-soft); }
.callout.good { background: var(--good-soft); }

.scroll { overflow-x: auto; -webkit-overflow-scrolling: touch; border: 1px solid var(--line); border-radius: 14px; background: var(--surface); margin: 14px 0; }
table { border-collapse: collapse; width: 100%; font-size: .95rem; }
.scroll table { min-width: 600px; }
th { text-align: left; font-size: .82rem; color: var(--muted); font-weight: 700; padding: 12px 14px; border-bottom: 2px solid var(--line); }
td { padding: 12px 14px; border-bottom: 1px solid var(--line); vertical-align: top; }
tr:last-child td { border-bottom: 0; }
td.r, th.r { text-align: right; white-space: nowrap; font-variant-numeric: tabular-nums; }
tr.hl td { background: var(--red-soft); font-weight: 600; }
.yes { color: var(--good); font-weight: 600; }
.no { color: var(--bad); }

.steps { counter-reset: s; }
.steps .card { position: relative; padding-top: 48px; }
.steps .card::before { counter-increment: s; content: counter(s); position: absolute; top: 16px; left: 20px; width: 26px; height: 26px; border-radius: 50%; background: var(--red); color: var(--on-red); font-weight: 800; display: grid; place-items: center; font-size: .9rem; }

details { background: var(--surface); border: 1px solid var(--line); border-radius: 12px; padding: 0 18px; margin-bottom: 8px; }
summary { cursor: pointer; font-weight: 700; padding: 15px 0; list-style: none; display: flex; justify-content: space-between; gap: 12px; }
summary::-webkit-details-marker { display: none; }
summary::after { content: "+"; color: var(--red); font-size: 1.3rem; line-height: 1; }
details[open] summary::after { content: "–"; }
details p { padding-bottom: 14px; margin: 0; }

.cta-band { background: var(--ink); color: var(--bg); border-radius: 20px; padding: 32px 24px; margin-top: 56px; display: grid; gap: 14px; justify-items: start; }
.cta-band h2 { color: inherit; }

/* form */
form.f { display: grid; gap: 16px; }
label { display: block; font-weight: 600; font-size: .95rem; margin-bottom: 5px; }
input, select, textarea { width: 100%; padding: 12px 13px; border: 1.5px solid var(--line); border-radius: 10px; background: var(--surface); color: var(--ink); font: inherit; }
textarea { min-height: 90px; }
.chips { display: flex; flex-wrap: wrap; gap: 8px; }
.chips label { display: inline-flex; align-items: center; gap: 8px; margin: 0; font-weight: 500; border: 1.5px solid var(--line); border-radius: 99px; padding: 8px 14px; background: var(--surface); cursor: pointer; }
.chips input { width: auto; accent-color: var(--red); }
.hp { position: absolute; left: -9999px; }
.err { color: var(--bad); font-weight: 600; }
.ok { color: var(--good); font-weight: 600; }

footer { margin-top: 64px; border-top: 1px solid var(--line); padding-block: 28px 40px; font-size: .9rem; color: var(--muted); }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }