:root{
  --bg:#ECF1EC;        /* giấy lụa xanh nhạt */
  --paper:#FBFCF9;
  --ink:#1D2B2A;
  --muted:#5E6E6B;
  --jade:#2F6F62;
  --jade-soft:#D3E5DE;
  --cinnabar:#B8432F;
  --cinnabar-soft:#F3D9D2;
  --gold:#C9952B;
  --line:#C6D3CD;
  --hz:"Noto Serif SC","Songti SC","SimSun",serif;
  --ui:"Be Vietnam Pro",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;
  --r-sm:8px; --r-lg:18px;
  --nav-h:72px;
}
*{box-sizing:border-box}
html,body{margin:0;min-height:100%}
html{background:var(--bg)}
body{
  background:var(--bg);color:var(--ink);font:16px/1.5 var(--ui);
  padding-bottom:calc(var(--nav-h) + 8px);
  -webkit-tap-highlight-color:transparent;
}
button,input,select{font:inherit;color:inherit}
button{cursor:pointer}
:focus-visible{outline:3px solid var(--gold);outline-offset:2px}
.sr{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0)}

/* header */
.top{
  position:sticky;top:0;z-index:5;background:var(--bg);
  padding:calc(10px + env(safe-area-inset-top,0px)) 16px 10px;
  border-bottom:1px solid var(--line);
  display:flex;flex-wrap:wrap;gap:10px 16px;align-items:center;justify-content:space-between;
}
.brand{display:flex;align-items:center;gap:10px;font-weight:700;font-size:17px}
.seal{
  font-family:var(--hz);background:var(--cinnabar);color:#fff;width:32px;height:32px;
  display:grid;place-items:center;border-radius:6px;font-size:20px;transform:rotate(-4deg)
}
.filters{display:flex;gap:10px;align-items:center;flex-wrap:wrap}
.sel select{
  appearance:none;background:var(--paper) url("data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' width='12' height='8'><path d='M1 1l5 5 5-5' fill='none' stroke='%232F6F62' stroke-width='2'/></svg>") no-repeat right 12px center;
  border:1px solid var(--line);border-radius:var(--r-sm);padding:8px 34px 8px 12px;max-width:62vw;font-weight:500
}
.levels{display:flex;gap:4px}
.levels button{
  border:1px solid var(--line);background:var(--paper);border-radius:999px;padding:5px 10px;font-size:13px;font-weight:600;color:var(--muted)
}
.levels button[aria-pressed=true]{background:var(--jade);border-color:var(--jade);color:#fff}

main{max-width:640px;margin:0 auto;padding:20px 16px 28px;outline:none}
h2{font-size:20px;margin:0 0 4px}
.sub{color:var(--muted);margin:0 0 18px;font-size:14px}

/* bottom tabs */
.tabs{
  position:fixed;left:0;right:0;bottom:0;z-index:6;display:flex;background:var(--paper);
  border-top:1px solid var(--line);padding-bottom:env(safe-area-inset-bottom,0px)
}
.tabs button{
  flex:1;border:0;background:none;padding:8px 2px 10px;font-size:11.5px;white-space:nowrap;color:var(--muted);
  display:flex;flex-direction:column;align-items:center;gap:2px
}
.tabs .ic{font-family:var(--hz);font-size:20px;line-height:1.2}
.tabs button[aria-current=page]{color:var(--jade);font-weight:600}
.tabs button[aria-current=page] .ic{color:var(--cinnabar)}
/* thanh nút hành động luôn nằm ngay trên thanh tab */
.dock{
  position:sticky;bottom:var(--nav-h);z-index:4;
  background:linear-gradient(to bottom,rgba(236,241,236,0),var(--bg) 14px);
  padding:16px 0 10px;margin-top:4px
}
.actions.dock{margin-top:8px}

/* điện thoại: header gọn và không dính, nhường chỗ cho nội dung */
@media (max-width:600px){
  .top{position:static;padding:calc(8px + env(safe-area-inset-top,0px)) 12px 8px;gap:8px}
  .brand{display:none}
  .filters{width:100%}
  .sel{flex:1 1 100%}
  .sel select{max-width:none;width:100%;padding:7px 34px 7px 12px}
  .levels button{padding:4px 9px}
  main{padding:14px 12px 8px}
  h2{font-size:18px}
  .sub{margin-bottom:12px}
  .bar{margin-bottom:12px}
  .prompt{padding:14px;margin-bottom:10px}
  .prompt .hz{font-size:clamp(44px,15vw,64px)}
  .opts{gap:8px}
  .opt{min-height:48px;padding:11px 14px}
  .opt.hzopt{font-size:26px}
  .card{min-height:340px}
  .grid-cell{width:min(56vw,210px)}
  .fb{min-height:22px;margin-top:6px;font-size:15px}
}
@media (max-width:600px) and (max-height:700px){
  .prompt .hz{font-size:44px}
  .card{min-height:300px}
}

@media (min-width:900px){
  body{padding-bottom:0;padding-left:96px}
  .dock{bottom:0}
  .tabs{top:0;right:auto;width:96px;flex-direction:column;justify-content:center;border-top:0;border-right:1px solid var(--line)}
  .tabs button{flex:0;padding:14px 4px}
}

/* 田字格 — điểm nhấn chính */
.grid-cell{
  position:relative;width:min(62vw,240px);aspect-ratio:1;margin:0 auto;
  border:2px solid var(--cinnabar);background:var(--paper);
  display:grid;place-items:center;
  background-image:
    linear-gradient(to right,transparent calc(50% - .5px),var(--cinnabar-soft) calc(50% - .5px),var(--cinnabar-soft) calc(50% + .5px),transparent calc(50% + .5px)),
    linear-gradient(to bottom,transparent calc(50% - .5px),var(--cinnabar-soft) calc(50% - .5px),var(--cinnabar-soft) calc(50% + .5px),transparent calc(50% + .5px));
}
.hz{font-family:var(--hz);font-weight:700;line-height:1}
.grid-cell .hz{font-size:clamp(48px,calc(var(--fit,1) * 1px),132px)}

/* flashcard */
.card-wrap{perspective:1200px}
.card{
  position:relative;min-height:400px;transform-style:preserve-3d;transition:transform .5s ease;cursor:pointer;
}
.card.flip{transform:rotateY(180deg)}
.face{
  position:absolute;inset:0;backface-visibility:hidden;-webkit-backface-visibility:hidden;
  background:var(--paper);border:1px solid var(--line);border-radius:var(--r-lg);
  display:flex;flex-direction:column;align-items:center;justify-content:center;gap:16px;padding:24px;text-align:center
}
.face.back{transform:rotateY(180deg)}
.hint{font-size:13px;color:var(--muted)}
.py{font-size:26px;font-weight:600;color:var(--jade)}
.mean{font-size:20px;font-weight:500;max-width:30ch}
.tag{font-size:12px;color:var(--muted);border:1px solid var(--line);border-radius:999px;padding:2px 10px}
.back .hz{font-size:56px}
.row{display:flex;gap:10px;align-items:center;justify-content:center;flex-wrap:wrap}
.count{font-variant-numeric:tabular-nums;color:var(--muted);font-size:14px}

.btn{
  border:1px solid var(--line);background:var(--paper);border-radius:var(--r-sm);padding:12px 18px;font-weight:600;min-height:48px
}
.btn.primary{background:var(--jade);border-color:var(--jade);color:#fff}
.btn.danger{color:var(--cinnabar);border-color:var(--cinnabar)}
.btn.wide{flex:1}
.btn:disabled{opacity:.45;cursor:default}
.speak{
  width:48px;height:48px;border-radius:50%;border:1px solid var(--line);background:var(--paper);
  display:inline-grid;place-items:center;flex:none
}
.speak svg{width:22px;height:22px;fill:var(--jade)}
.actions{display:flex;gap:10px;margin-top:16px}

/* quiz */
.bar{height:6px;background:var(--jade-soft);border-radius:999px;overflow:hidden;margin-bottom:18px}
.bar i{display:block;height:100%;background:var(--jade);transition:width .3s}
.prompt{background:var(--paper);border:1px solid var(--line);border-radius:var(--r-lg);padding:22px;text-align:center;margin-bottom:14px}
.prompt .q{font-size:14px;color:var(--muted);margin-bottom:10px}
.prompt .hz{font-size:72px}
.prompt .mean{margin:0 auto}
.opts{display:grid;gap:10px}
.opt{
  text-align:left;border:1px solid var(--line);background:var(--paper);border-radius:var(--r-sm);padding:14px 16px;min-height:56px;font-weight:500
}
.opt.hzopt{text-align:center;font-family:var(--hz);font-size:30px;font-weight:700;padding:8px}
.opts.hzgrid{grid-template-columns:1fr 1fr}
.opt.ok{background:var(--jade-soft);border-color:var(--jade)}
.opt.no{background:var(--cinnabar-soft);border-color:var(--cinnabar)}
.result{text-align:center;padding:30px 10px}
.score{font-family:var(--hz);font-size:84px;font-weight:700;color:var(--jade);line-height:1}

/* match */
.mhead{display:flex;justify-content:space-between;align-items:baseline;margin-bottom:14px}
.timer{font-variant-numeric:tabular-nums;font-size:28px;font-weight:700}
.tiles{display:grid;grid-template-columns:repeat(3,1fr);gap:8px}
.tile{
  min-height:84px;border:1px solid var(--line);background:var(--paper);border-radius:var(--r-sm);padding:8px;
  font-size:14px;font-weight:500;line-height:1.3;transition:opacity .25s,transform .25s
}
.tile.hzt{font-family:var(--hz);font-size:30px;font-weight:700}
.tile.sel{border-color:var(--jade);box-shadow:inset 0 0 0 2px var(--jade)}
.tile.gone{opacity:0;transform:scale(.85);pointer-events:none}
.tile.bad{animation:shake .35s}
@keyframes shake{25%{transform:translateX(-5px)}75%{transform:translateX(5px)}}

/* typing */
.seg{display:flex;background:var(--jade-soft);border-radius:var(--r-sm);padding:4px;margin-bottom:16px}
.seg button{flex:1;border:0;background:none;padding:8px;border-radius:6px;font-weight:600;color:var(--jade)}
.seg button[aria-pressed=true]{background:var(--paper);color:var(--ink)}
.answer{
  width:100%;border:2px solid var(--line);border-radius:var(--r-sm);padding:14px;font-size:24px;text-align:center;background:var(--paper)
}
.answer.hzin{font-family:var(--hz)}
.answer.ok{border-color:var(--jade)}
.answer.no{border-color:var(--cinnabar)}
.fb{min-height:28px;text-align:center;margin-top:10px;font-weight:600}
.fb.ok{color:var(--jade)} .fb.no{color:var(--cinnabar)}

/* stats */
.stat{display:grid;grid-template-columns:1fr auto;gap:4px 12px;padding:12px 0;border-bottom:1px solid var(--line)}
.stat .name{font-weight:500}
.stat .num{font-variant-numeric:tabular-nums;color:var(--muted);font-size:14px}
.stat .bar{grid-column:1/-1;margin:0}
.totals{display:flex;gap:24px;margin:6px 0 18px}
.totals b{display:block;font-size:28px;color:var(--jade)}
.totals span{font-size:13px;color:var(--muted)}

.empty{text-align:center;padding:40px 10px;color:var(--muted)}

#toast{
  position:fixed;left:50%;bottom:calc(84px + env(safe-area-inset-bottom,0px));transform:translateX(-50%) translateY(20px);
  background:var(--ink);color:#fff;padding:10px 16px;border-radius:var(--r-sm);font-size:14px;opacity:0;pointer-events:none;
  transition:opacity .2s,transform .2s;max-width:90vw;text-align:center;z-index:10
}
#toast.show{opacity:1;transform:translateX(-50%) translateY(0)}

@media (prefers-reduced-motion:reduce){*{transition:none!important;animation:none!important}}