:root {
  --ink: #1d2b3a;
  --ink-2: #4a5a6b;
  --muted: #7a8794;
  --bg: #fbf8f3;
  --card: #ffffff;
  --line: #ece5da;
  --brand: #1f4e9a;
  --brand-2: #e9f0fb;
  --coral: #f2704f;
  --coral-2: #fde9e3;
  --sun: #ffc845;
  --sun-2: #fff4d1;
  --mint: #2f9e74;
  --mint-2: #e2f4ec;
  --vi: #1f4e9a;
  --radius: 16px;
  --shadow: 0 1px 2px rgba(29, 43, 58, .06), 0 6px 20px rgba(29, 43, 58, .06);
  --font: "Be Vietnam Pro", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0; background: var(--bg); color: var(--ink);
  font: 16px/1.55 var(--font);
}
a { color: var(--brand); }
button { font: inherit; color: inherit; cursor: pointer; }
.wrap { max-width: 1040px; margin: 0 auto; padding: 0 16px; }

/* top bar */
.topbar { display: flex; align-items: center; gap: 10px; padding: 14px 0; }
.logo { display: flex; align-items: center; gap: 8px; font-weight: 800; color: var(--ink); text-decoration: none; letter-spacing: -.01em; }
.logo-mark { width: 30px; height: 30px; border-radius: 9px; background: var(--brand); display: grid; place-items: center; }
.logo-mark svg { width: 20px; height: 20px; }
.topbar .spacer { flex: 1; }
.pill { font-size: 13px; color: var(--ink-2); background: var(--card); border: 1px solid var(--line); border-radius: 99px; padding: 4px 10px; }

/* landing */
.hero { padding: 28px 0 8px; }
.hero h1 { font-size: clamp(28px, 6vw, 44px); line-height: 1.15; margin: 0 0 12px; letter-spacing: -.02em; }
.hero h1 em { font-style: normal; color: var(--coral); }
.hero p { color: var(--ink-2); font-size: 18px; margin: 0; max-width: 640px; }
.how { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; margin: 24px 0; }
.how div { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px; }
.how b { display: block; margin-bottom: 2px; }
.how span { color: var(--ink-2); font-size: 14px; }
.how .n { display: inline-grid; place-items: center; width: 26px; height: 26px; border-radius: 50%; background: var(--sun); font-weight: 800; font-size: 14px; margin-bottom: 8px; }
@media (max-width: 640px) { .how { grid-template-columns: 1fr; } }

.card { background: var(--card); border: 1px solid var(--line); border-radius: 20px; box-shadow: var(--shadow); padding: 20px; }
.drop { display: block;
  border: 2px dashed #d3c8b8; border-radius: var(--radius); padding: 32px 16px; text-align: center;
  background: #fffdf9; transition: .15s; cursor: pointer;
}
.drop.over { border-color: var(--brand); background: var(--brand-2); }
.drop .big { font-size: 20px; font-weight: 700; margin: 8px 0 4px; }
.drop .small { color: var(--muted); font-size: 14px; }
.drop svg { width: 44px; height: 44px; color: var(--brand); }
.file-chosen { margin-top: 12px; font-weight: 600; word-break: break-word; }
.consent { display: flex; gap: 10px; align-items: flex-start; margin: 16px 0; font-size: 14px; color: var(--ink-2); }
.consent input { width: 20px; height: 20px; margin-top: 2px; flex: none; accent-color: var(--brand); }
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px; border: 0; border-radius: 12px;
  background: var(--brand); color: #fff; font-weight: 700; padding: 13px 20px; font-size: 16px; text-decoration: none;
}
.btn:disabled { opacity: .45; cursor: not-allowed; }
.btn.ghost { background: var(--card); color: var(--ink); border: 1px solid var(--line); }
.btn.coral { background: var(--coral); }
.btn.block { width: 100%; }
.err { color: #b42318; background: #fef3f2; border-radius: 10px; padding: 10px 12px; margin-top: 12px; font-size: 14px; }

.steps { list-style: none; padding: 0; margin: 16px 0 0; }
.steps li { display: flex; gap: 10px; align-items: center; padding: 7px 0; color: var(--muted); }
.steps li .dot { width: 22px; height: 22px; border-radius: 50%; border: 2px solid var(--line); flex: none; display: grid; place-items: center; font-size: 12px; }
.steps li.on { color: var(--ink); font-weight: 600; }
.steps li.on .dot { border-color: var(--brand); border-top-color: transparent; animation: spin 1s linear infinite; }
.steps li.ok { color: var(--ink-2); }
.steps li.ok .dot { background: var(--mint); border-color: var(--mint); color: #fff; }
@keyframes spin { to { transform: rotate(360deg); } }
.bar { height: 6px; background: var(--line); border-radius: 9px; overflow: hidden; margin-top: 12px; }
.bar i { display: block; height: 100%; width: 0; background: var(--brand); transition: width .3s; }

.done-box { text-align: center; }
.done-box h2 { margin: 6px 0; }
.share { display: flex; gap: 8px; margin: 14px 0; }
.share input { flex: 1; min-width: 0; border: 1px solid var(--line); border-radius: 10px; padding: 10px; font: inherit; font-size: 14px; background: #fffdf9; }
#qr { display: inline-block; padding: 8px; background: #fff; border-radius: 12px; border: 1px solid var(--line); margin-top: 6px; }

.recent h3 { margin: 28px 0 10px; font-size: 18px; }
.recent a { display: flex; justify-content: space-between; gap: 10px; background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 12px 14px; text-decoration: none; color: var(--ink); margin-bottom: 8px; }
.recent a span { color: var(--muted); font-size: 13px; white-space: nowrap; }
.foot { color: var(--muted); font-size: 13px; padding: 28px 0 40px; }

/* lesson */
.lesson-head { padding: 4px 0 10px; }
.lesson-head .subj { color: var(--coral); font-weight: 700; font-size: 13px; text-transform: uppercase; letter-spacing: .04em; }
.lesson-head h1 { margin: 2px 0 0; font-size: clamp(22px, 4.5vw, 32px); line-height: 1.2; letter-spacing: -.01em; }
.lesson-head .vi { color: var(--vi); font-style: italic; margin-top: 2px; }
.tabs { display: flex; gap: 6px; background: #efe8dd; padding: 4px; border-radius: 14px; margin: 10px 0 14px; position: sticky; top: 6px; z-index: 20; }
.tabs button { flex: 1; border: 0; background: transparent; border-radius: 10px; padding: 9px 6px; font-weight: 700; font-size: 15px; color: var(--ink-2); }
.tabs button[aria-selected="true"] { background: var(--card); color: var(--ink); box-shadow: var(--shadow); }
.panel[hidden] { display: none; }

.toolbar { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin-bottom: 10px; }
.toolbar .grow { flex: 1; }
.nav { display: flex; align-items: center; gap: 6px; }
.iconbtn { width: 42px; height: 42px; border-radius: 12px; border: 1px solid var(--line); background: var(--card); display: grid; place-items: center; }
.iconbtn:disabled { opacity: .35; }
.iconbtn svg, .chip svg { width: 20px; height: 20px; }
.pageno { font-weight: 700; min-width: 64px; text-align: center; font-variant-numeric: tabular-nums; }
.chip { display: inline-flex; align-items: center; gap: 6px; border: 1px solid var(--line); background: var(--card); border-radius: 99px; padding: 8px 12px; font-size: 14px; font-weight: 600; }
.chip[aria-pressed="true"] { background: var(--brand); border-color: var(--brand); color: #fff; }
.chip.play { background: var(--coral); border-color: var(--coral); color: #fff; }

.stage { position: relative; border-radius: 14px; overflow: hidden; background: #fff; box-shadow: var(--shadow); touch-action: pan-y; }
.stage img { display: block; width: 100%; height: auto; user-select: none; -webkit-user-drag: none; }
.hs { position: absolute; border-radius: 6px; cursor: pointer; -webkit-tap-highlight-color: transparent; }
.hs.sent { z-index: 1; }
.hs.word { z-index: 2; border-radius: 4px; }
.show-hs .hs.sent { outline: 2px dashed rgba(31, 78, 154, .35); outline-offset: -1px; }
.show-hs .hs.word { box-shadow: inset 0 -4px 0 rgba(255, 200, 69, .85); }
.hs.sent:hover { background: rgba(31, 78, 154, .07); }
.hs.word:hover { background: rgba(255, 200, 69, .3); }
.hs.active { background: rgba(255, 200, 69, .38) !important; outline: 2px solid var(--sun) !important; }
.hs.word.active { background: rgba(242, 112, 79, .3) !important; outline-color: var(--coral) !important; }

.sub { min-height: 74px; margin-top: 10px; background: var(--ink); color: #fff; border-radius: 14px; padding: 12px 16px; }
.sub .en { font-weight: 700; font-size: 18px; }
.sub .vi { color: #c9dbff; font-style: italic; margin-top: 2px; }
.sub .hint { color: #b6c2cf; font-size: 15px; }
.sub .kwmean { display: inline-block; margin-top: 4px; background: var(--sun); color: var(--ink); border-radius: 8px; padding: 2px 8px; font-weight: 700; font-style: normal; }
.hide-vi .sub .vi, .hide-vi .ulist .vi { display: none; }

.ulist { list-style: none; padding: 0; margin: 14px 0 0; display: grid; gap: 8px; }
.ulist li { display: flex; gap: 10px; align-items: flex-start; background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 10px 12px; cursor: pointer; }
.ulist li.active { border-color: var(--sun); background: var(--sun-2); }
.ulist .spk { flex: none; width: 34px; height: 34px; border-radius: 50%; border: 0; background: var(--brand-2); color: var(--brand); display: grid; place-items: center; }
.ulist .spk svg { width: 18px; height: 18px; }
.ulist .en { font-weight: 600; }
.ulist .vi { color: var(--vi); font-style: italic; font-size: 15px; }
.section-label { font-size: 13px; color: var(--muted); font-weight: 700; text-transform: uppercase; letter-spacing: .05em; margin-top: 18px; }

.kwgrid { display: grid; grid-template-columns: repeat(auto-fill, minmax(160px, 1fr)); gap: 10px; }
.kw { text-align: left; background: var(--card); border: 1px solid var(--line); border-radius: 14px; padding: 12px; display: flex; flex-direction: column; gap: 2px; }
.kw:nth-child(4n+1) { background: #fff3e8; } .kw:nth-child(4n+2) { background: var(--sun-2); }
.kw:nth-child(4n+3) { background: var(--mint-2); } .kw:nth-child(4n+4) { background: var(--brand-2); }
.kw .w { font-size: 22px; font-weight: 800; display: flex; align-items: center; gap: 6px; }
.kw .w svg { width: 18px; height: 18px; color: var(--ink-2); }
.kw .m { color: var(--vi); font-weight: 700; }
.kw .x { color: var(--ink-2); font-size: 14px; }
.kw.active { outline: 3px solid var(--coral); }

.quiz { margin-top: 18px; text-align: center; }
.quiz .q { font-size: 18px; margin: 10px 0; }
.quiz .opts { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; max-width: 520px; margin: 0 auto; }
.quiz .opts button { border: 2px solid var(--line); background: var(--card); border-radius: 14px; padding: 14px; font-size: 20px; font-weight: 800; }
.quiz .opts button.right { border-color: var(--mint); background: var(--mint-2); }
.quiz .opts button.wrong { border-color: var(--coral); background: var(--coral-2); }
.quiz .score { color: var(--ink-2); margin-top: 10px; }

.guide h2 { font-size: 20px; margin: 22px 0 8px; }
.guide h2:first-child { margin-top: 0; }
.guide ul { margin: 0; padding-left: 20px; }
.guide li { margin: 4px 0; }
.act { background: var(--card); border: 1px solid var(--line); border-radius: 14px; padding: 14px; margin-bottom: 10px; }
.act b { display: block; font-size: 17px; }
.act .mat { color: var(--ink-2); font-size: 14px; margin: 2px 0 6px; }
.act ol { margin: 0; padding-left: 20px; }
.qa { display: flex; gap: 10px; align-items: flex-start; padding: 8px 0; border-bottom: 1px solid var(--line); }
.qa .vi { color: var(--vi); font-style: italic; font-size: 15px; }
.downloads { display: flex; flex-wrap: wrap; gap: 8px; margin: 20px 0 8px; }
.note { color: var(--muted); font-size: 13px; }
.center { text-align: center; padding: 60px 16px; color: var(--ink-2); }

@media print {
  .topbar, .tabs, .toolbar, .downloads, .noprint { display: none !important; }
  body { background: #fff; }
  .panel[hidden] { display: none !important; }
}