:root{
  --bg:#0f1115; --bg2:#12151b; --panel:#171a21; --panel2:#1e2230; --text:#e6e8ee;
  --muted:#8b92a3; --line:#2a2f3d; --line2:#353b4d; --accent:#58a6ff; --accent2:#79c0ff;
  --green:#3fb950; --red:#f85149; --blank:#3b4252; --amber:#d29922;
  --radius:12px; --radius-lg:16px;
  --shadow:0 1px 2px rgba(0,0,0,.35), 0 8px 24px -16px rgba(0,0,0,.7);
  --ring:0 0 0 3px rgba(88,166,255,.28);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
  background:radial-gradient(1200px 600px at 50% -200px,rgba(88,166,255,.10),transparent 70%) var(--bg);
  color:var(--text);line-height:1.55;-webkit-font-smoothing:antialiased;
}

/* ------------------------------- top bar ------------------------------- */
header{position:sticky;top:0;z-index:50;background:rgba(15,17,21,.9);backdrop-filter:blur(10px);border-bottom:1px solid var(--line);padding:12px 20px 10px}
header.idle{display:none}
.hrow{display:flex;align-items:center;gap:12px;flex-wrap:wrap}
.push-down{margin-top:8px}
.topicbar{font-size:12.5px;font-weight:700;color:var(--text);white-space:nowrap;overflow:hidden;text-overflow:ellipsis;max-width:46vw}
.bar{flex:1 1 200px;height:12px;background:var(--blank);border-radius:8px;overflow:hidden;display:flex}
.bar .seg-g{background:var(--green);height:100%;width:0;transition:width .25s}
.bar .seg-r{background:var(--red);height:100%;width:0;transition:width .25s}
.bar-thin{flex:1 1 200px;height:8px;background:var(--blank);border-radius:6px;overflow:hidden}
.bar-thin>div{height:100%;width:0;background:linear-gradient(90deg,var(--accent),var(--accent2));transition:width .25s}
.meta{font-size:13px;color:var(--muted);white-space:nowrap;display:flex;gap:14px;align-items:center}
.meta b{color:var(--text)}
#timer{font-variant-numeric:tabular-nums;font-weight:800;color:var(--text);background:var(--panel2);border:1px solid var(--line);border-radius:8px;padding:2px 9px}
#circles{display:flex;gap:6px;flex-wrap:wrap;margin-top:10px}
.c{width:26px;height:26px;border-radius:50%;display:flex;align-items:center;justify-content:center;background:var(--blank);color:#cdd3e0;font-size:11px;font-weight:700;cursor:pointer;border:2px solid transparent;transition:transform .15s,border-color .15s}
.c:hover{transform:scale(1.12);border-color:#fff}
.c.cur{border-color:var(--accent);box-shadow:0 0 0 3px rgba(88,166,255,.2)}
.c.pass{background:var(--green);color:#04260f}
.c.fail{background:var(--red);color:#330403}
.c.todo{opacity:.45;cursor:default}
.c.todo:hover{transform:none;border-color:transparent}

/* --------------------------------- layout --------------------------------- */
main{max-width:1080px;margin:22px auto;padding:0 18px 90px}

/* home: brand, hero, grouped rows of four */
.brandbar{display:flex;align-items:center;gap:14px;padding:2px 2px 14px}
.brandbar .mark{flex:none;width:44px;height:44px;border-radius:12px;display:flex;align-items:center;justify-content:center;font-weight:800;font-size:15px;letter-spacing:.5px;color:#04121f;background:linear-gradient(135deg,var(--accent),#7ee2a8);box-shadow:var(--shadow)}
.brandbar h1{margin:0;font-size:19px;font-weight:800;letter-spacing:-.2px}
.brandbar p{margin:2px 0 0;color:var(--muted);font-size:13px}
.hero{background:linear-gradient(180deg,var(--panel2),var(--panel));border:1px solid var(--line);border-radius:var(--radius-lg);padding:18px 20px;margin-bottom:22px;box-shadow:var(--shadow)}
.hero h2{margin:0 0 6px;font-size:21px;letter-spacing:-.3px}
.hero p{margin:0;color:var(--muted);font-size:14px}
.tgroup{margin-bottom:26px}
.ghead{display:flex;align-items:baseline;gap:10px;flex-wrap:wrap;margin:0 0 12px;padding-bottom:8px;border-bottom:1px solid var(--line)}
.ghead h3{margin:0;font-size:13px;font-weight:800;text-transform:uppercase;letter-spacing:.09em;color:var(--accent)}
.ghead span{font-size:12.5px;color:var(--muted)}
/* Every section holds four topics, so the column count has to divide four:
   4 across, then 2, then 1. (Three columns would leave a 3+1 row in each.) */
.grid{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:14px}
@media(max-width:1080px){.grid{grid-template-columns:repeat(2,minmax(0,1fr))}}
@media(max-width:520px){.grid{grid-template-columns:1fr}}

.card{
  display:flex;flex-direction:column;min-height:172px;background:linear-gradient(180deg,var(--panel2),var(--panel));
  border:1px solid var(--line);border-radius:var(--radius);padding:15px;cursor:pointer;box-shadow:var(--shadow);
  transition:transform .14s,border-color .14s,box-shadow .14s;
}
.card:hover{transform:translateY(-3px);border-color:var(--accent);box-shadow:0 10px 30px -18px rgba(88,166,255,.7)}
.card:focus-visible{outline:none;border-color:var(--accent);box-shadow:var(--ring)}
.card .chead{display:flex;align-items:flex-start;justify-content:space-between;gap:8px;margin-bottom:6px}
.card h3{margin:0;font-size:15px;line-height:1.3}
.chip{flex:none;font-size:10.5px;font-weight:700;color:var(--accent);background:rgba(88,166,255,.12);border:1px solid rgba(88,166,255,.3);border-radius:999px;padding:1px 7px;white-space:nowrap}
.card p{margin:0;font-size:12.5px;color:var(--muted);display:-webkit-box;-webkit-line-clamp:3;-webkit-box-orient:vertical;overflow:hidden}
.card .cfoot{margin-top:auto;padding-top:10px;display:flex;align-items:center;gap:8px;flex-wrap:wrap;font-size:11.5px;color:var(--muted)}
.card .stat{white-space:nowrap}
.card .badges{margin-left:auto;display:flex;gap:6px;flex-wrap:wrap}
.badge{font-size:11px;font-weight:700;border-radius:999px;padding:1px 8px;white-space:nowrap}
.badge.resume{color:#04121f;background:var(--accent)}
.badge.best{color:var(--green);border:1px solid rgba(63,185,80,.45);background:rgba(63,185,80,.1)}

/* --------------------------------- setup --------------------------------- */
.setup{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius-lg);padding:24px;max-width:600px;margin:0 auto;box-shadow:var(--shadow)}
.setup h3{margin:0 0 4px;font-size:16px}
.setup p{margin:0 0 14px;color:var(--muted);font-size:14px}
.mixrow{display:flex;align-items:center;gap:12px;justify-content:center;margin:12px 0 10px;flex-wrap:wrap}
.mixrow label{font-size:14px;font-weight:700}
#mixInput{width:96px;background:#0b0d11;color:var(--text);border:1px solid var(--line2);border-radius:10px;padding:9px 12px;font:inherit;font-size:16px;font-weight:700;text-align:center}
#mixInput:focus{outline:none;border-color:var(--accent);box-shadow:var(--ring)}
.mixtext{font-size:14px;color:var(--muted)}
.mixtext b{color:var(--accent)}
.mixquick{display:flex;gap:10px;justify-content:center;flex-wrap:wrap;margin-bottom:16px}
.mixquick .btn{padding:6px 12px;font-size:12px}
.gradingnote{background:var(--panel2);border:1px solid var(--line);border-radius:10px;padding:11px 13px;font-size:12.5px;color:var(--muted);line-height:1.55}
.gradingnote+.gradingnote{margin-top:10px}
.gradingnote b{color:var(--text)}
.gradingnote code{background:rgba(0,0,0,.35);border-radius:4px;padding:0 4px}
.aitoggle{display:flex;gap:10px;align-items:flex-start;font-size:12.5px;color:var(--muted);line-height:1.55;cursor:pointer}
.aitoggle input{margin-top:2px;accent-color:var(--accent)}

/* --------------------------------- quiz --------------------------------- */
.q{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius-lg);padding:18px;margin-bottom:18px;scroll-margin-top:180px;box-shadow:var(--shadow)}
.qhead{display:flex;justify-content:space-between;align-items:center;gap:10px;border-bottom:1px solid var(--line);padding-bottom:10px;margin-bottom:12px;flex-wrap:wrap}
.qnum{font-weight:800;font-size:14px;color:var(--accent)}
.qtag{font-size:11.5px;color:var(--muted);background:var(--panel2);border:1px solid var(--line);border-radius:999px;padding:2px 9px}
.prompt{font-size:15.5px;margin:10px 0 4px}
.prompt code{background:#0b0d11;border:1px solid var(--line);border-radius:5px;padding:1px 6px;font-size:13px}
pre.code{background:#0b0d11;border:1px solid var(--line);border-radius:10px;padding:12px;overflow:auto;font-size:13px}
.opts{display:grid;gap:10px;margin-top:14px}
.opt{text-align:left;background:var(--panel2);border:1px solid var(--line);color:var(--text);border-radius:10px;padding:11px 13px;font-size:14px;cursor:pointer;display:flex;gap:10px;align-items:flex-start;line-height:1.45;transition:border-color .12s,background .12s,transform .12s}
.opt:hover:not(:disabled){border-color:var(--accent);transform:translateX(2px)}
.opt:focus-visible{outline:none;box-shadow:var(--ring)}
.opt:disabled{cursor:default;opacity:1}
.opt .k{flex:none;width:24px;height:24px;border-radius:8px;background:var(--blank);display:flex;align-items:center;justify-content:center;font-size:12px;font-weight:800}
.opt code{background:rgba(0,0,0,.3);border-radius:4px;padding:0 5px;font-size:13px}
.opt.sel{border-color:var(--accent);background:rgba(88,166,255,.12)}
.opt.right{border-color:var(--green);background:rgba(63,185,80,.12)}
.opt.right .k{background:var(--green);color:#04260f}
.opt.wrong{border-color:var(--red);background:rgba(248,81,73,.12)}
.opt.wrong .k{background:var(--red);color:#330403}
.opt.dim{opacity:.55}
.runnote{font-size:12px;color:var(--muted);margin:12px 0 0}
.runnote.remote{color:var(--amber);border-left:2px solid rgba(210,153,34,.6);padding-left:9px}
.engine{font-size:13px;color:var(--amber);margin-top:8px;white-space:pre-wrap}
.engine.warn{color:#ffa198;background:rgba(248,81,73,.08);border:1px solid rgba(248,81,73,.3);border-radius:10px;padding:9px 11px}
#ta{width:100%;min-height:64px;background:#0b0d11;color:var(--text);border:1px solid var(--line2);border-radius:10px;padding:10px 12px;font:inherit;font-size:14px;resize:vertical;margin-top:12px}
#ta:focus{outline:none;border-color:var(--accent);box-shadow:var(--ring)}
#ta.codeta{font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;font-size:13px;min-height:200px;line-height:1.5}
.blanks{display:grid;gap:10px;margin-top:12px}
.blabel{display:grid;gap:4px;font-size:13px;color:var(--muted)}
.blank{background:#0b0d11;color:var(--text);border:1px solid var(--line2);border-radius:10px;padding:9px 12px;font:inherit;font-size:14px;width:100%}
.blank:focus{outline:none;border-color:var(--accent);box-shadow:var(--ring)}

/* feedback */
.feed{margin-top:14px;border-radius:10px;padding:11px 13px;font-size:14px;display:none}
.feed.show{display:block}
.feed.g{background:rgba(63,185,80,.1);border:1px solid rgba(63,185,80,.35);color:#7ee787}
.feed.r{background:rgba(248,81,73,.1);border:1px solid rgba(248,81,73,.35);color:#ffa198}
.feed .why{color:var(--text);margin-top:6px;display:block}
.feed .why code{background:rgba(0,0,0,.35);border-radius:4px;padding:0 5px;font-size:13px}
.feed .time{color:var(--muted);font-size:13px}
.hintline{color:var(--amber)}
.feed .hintline{color:var(--amber)}
.softline{color:#7ee2a8}
.ailine{color:#a5b4fc}
.pick-note{color:var(--muted)}
.airow{display:flex;flex-wrap:wrap;align-items:center;gap:10px;margin-top:10px}
.aiout{margin-top:10px;font-size:12.5px;line-height:1.5;color:var(--muted);background:rgba(255,255,255,.03);border:1px solid var(--line);border-radius:10px;padding:9px 11px}
.aiout.small{font-size:12px}
.aiout.good{color:#7ee2a8;border-color:rgba(126,226,168,.35);background:rgba(126,226,168,.07)}
.aiout.bad{color:#ffa198;border-color:rgba(248,81,73,.3);background:rgba(248,81,73,.07)}
.ainote{font-size:12px;color:var(--muted)}

/* buttons */
.nav{display:flex;gap:10px;margin-top:16px;flex-wrap:wrap;align-items:center}
button{font:inherit}
.btn{background:var(--accent);color:#04121f;border:none;border-radius:10px;padding:10px 17px;font-size:13px;font-weight:700;cursor:pointer;box-shadow:var(--shadow);transition:filter .12s,transform .12s}
.btn:hover{filter:brightness(1.08);transform:translateY(-1px)}
.btn:focus-visible{outline:none;box-shadow:var(--ring)}
.btn:disabled{opacity:.45;cursor:not-allowed;transform:none;filter:none}
.btn.ghost{background:transparent;color:var(--accent);border:1px solid var(--accent);box-shadow:none}
.btn.ghost:hover{background:rgba(88,166,255,.1)}
.btn.sm{padding:5px 11px;font-size:12px}

/* -------------------------------- results -------------------------------- */
.result{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius-lg);padding:26px;text-align:center;box-shadow:var(--shadow)}
.result h2{margin:0 0 8px;font-size:23px;letter-spacing:-.3px}
.result .score{font-size:46px;font-weight:800;margin:8px 0;letter-spacing:-1px}
.result .sub{color:var(--muted);font-size:14px}
.rev{text-align:left;margin-top:20px;display:grid;gap:10px}
.rev-item{background:var(--panel2);border:1px solid var(--line);border-radius:10px;padding:10px 13px;font-size:13px}
.rev-item b.g{color:var(--green)}
.rev-item b.r{color:var(--red)}
.rev-item small{color:var(--muted)}
.rev-item .rq{margin:6px 0;font-size:14px}
.rev-item .rq code{background:rgba(0,0,0,.3);border-radius:4px;padding:0 5px;font-size:13px}
.rev-item pre.code{background:#0b0d11;border:1px solid var(--line);border-radius:10px;padding:10px;overflow:auto;font-size:12px;margin:8px 0}

.hidden{display:none}
footer{text-align:center;color:var(--muted);font-size:12px;padding:20px}
@media(max-width:560px){
  .meta{gap:8px}
  .topicbar{max-width:100%}
  .brandbar{align-items:flex-start}
  main{padding:0 14px 80px}
}
@media(prefers-reduced-motion:reduce){
  *{transition:none!important;animation:none!important}
  html{scroll-behavior:auto}
}