:root{
  --bg:#0f172a; --bg2:#1e293b; --card:#ffffff; --ink:#1e293b; --muted:#64748b;
  --line:#e2e8f0; --brand:#4f46e5; --brand2:#7c3aed; --accent:#0ea5e9;
  --ok:#16a34a; --okbg:#dcfce7; --bad:#dc2626; --badbg:#fee2e2; --warn:#d97706;
  --soft:#f8fafc; --shadow:0 1px 3px rgba(15,23,42,.08),0 8px 24px rgba(15,23,42,.06);
  --radius:14px;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,"PingFang SC","Microsoft YaHei",sans-serif;
  color:var(--ink);background:var(--soft);line-height:1.6;-webkit-font-smoothing:antialiased}
a{color:var(--brand);text-decoration:none}
a:hover{text-decoration:underline}
.container{max-width:1080px;margin:0 auto;padding:0 20px}

/* Header */
.topbar{background:linear-gradient(135deg,var(--bg) 0%,#312e81 100%);color:#fff;position:sticky;top:0;z-index:50;box-shadow:var(--shadow)}
.topbar .container{display:flex;align-items:center;gap:18px;height:60px}
.brand{font-weight:700;font-size:18px;color:#fff;display:flex;align-items:center;gap:9px}
.brand .logo{width:30px;height:30px;border-radius:8px;background:linear-gradient(135deg,var(--accent),var(--brand2));display:grid;place-items:center;font-size:16px}
.nav{margin-left:auto;display:flex;gap:6px;flex-wrap:wrap}
.nav a{color:#cbd5e1;padding:7px 13px;border-radius:9px;font-size:14px;font-weight:500}
.nav a:hover{background:rgba(255,255,255,.1);color:#fff;text-decoration:none}
.nav a.active{background:rgba(255,255,255,.16);color:#fff}

/* Hero */
.hero{background:linear-gradient(135deg,#312e81,#1e1b4b);color:#fff;padding:54px 0 60px}
.hero h1{font-size:40px;margin:0 0 8px;line-height:1.15}
.hero .sub{font-size:19px;color:#c7d2fe;margin:0 0 22px}
.hero .meta{display:flex;gap:10px;flex-wrap:wrap;margin-top:18px}
.pill{background:rgba(255,255,255,.12);border:1px solid rgba(255,255,255,.18);color:#e0e7ff;
  padding:6px 14px;border-radius:999px;font-size:13.5px}
.cta{display:inline-flex;gap:10px;margin-top:26px;flex-wrap:wrap}
.btn{display:inline-flex;align-items:center;gap:8px;background:var(--brand);color:#fff;border:none;
  padding:12px 22px;border-radius:11px;font-size:15px;font-weight:600;cursor:pointer;transition:.15s}
.btn:hover{background:var(--brand2);text-decoration:none;transform:translateY(-1px)}
.btn.ghost{background:rgba(255,255,255,.1);border:1px solid rgba(255,255,255,.25)}
.btn.lg{padding:14px 26px;font-size:16px}

/* Sections */
section.block{padding:40px 0}
h2.sec{font-size:26px;margin:0 0 6px}
.lead{color:var(--muted);margin:0 0 26px;font-size:16px}

/* Cards grid */
.grid{display:grid;gap:18px}
.grid.cards{grid-template-columns:repeat(auto-fill,minmax(300px,1fr))}
.card{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);padding:22px;box-shadow:var(--shadow);transition:.15s;display:flex;flex-direction:column}
.card:hover{transform:translateY(-3px);box-shadow:0 12px 30px rgba(15,23,42,.12)}
.card .num{font-size:13px;font-weight:700;color:var(--brand);letter-spacing:.04em;text-transform:uppercase}
.card h3{margin:6px 0 6px;font-size:19px}
.card .sections-tag{font-size:13px;color:var(--muted);margin-bottom:10px}
.card .desc{font-size:14.5px;color:#475569;flex:1}
.card .foot{display:flex;align-items:center;justify-content:space-between;margin-top:16px;padding-top:14px;border-top:1px solid var(--line)}
.qcount{font-size:13px;color:var(--muted)}
.card .go{font-size:14px;font-weight:600}

/* Lesson plan detail */
.lp{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow);margin-bottom:26px;overflow:hidden}
.lp-head{background:linear-gradient(135deg,#eef2ff,#faf5ff);padding:22px 24px;border-bottom:1px solid var(--line)}
.lp-head .num{font-size:13px;font-weight:700;color:var(--brand);text-transform:uppercase;letter-spacing:.04em}
.lp-head h3{margin:4px 0 4px;font-size:23px}
.lp-head .sections-tag{color:var(--muted);font-size:14px}
.lp-head .big{margin-top:10px;font-size:15px;color:#475569;font-style:italic}
.lp-body{padding:22px 24px}
.lp-body h4{font-size:15px;text-transform:uppercase;letter-spacing:.03em;color:var(--brand2);margin:18px 0 10px}
.lp-body h4:first-child{margin-top:0}
.obj{margin:0;padding-left:20px}
.obj li{margin:5px 0}
.timeline{border-left:2px solid var(--line);margin-left:6px;padding-left:0}
.tl-item{position:relative;padding:6px 0 14px 22px}
.tl-item::before{content:"";position:absolute;left:-7px;top:11px;width:12px;height:12px;border-radius:50%;background:var(--brand);border:2px solid #fff}
.tl-item.brk::before{background:var(--warn)}
.tl-time{font-size:12.5px;font-weight:700;color:var(--brand);font-variant-numeric:tabular-nums}
.tl-what{font-weight:600}
.tl-detail{font-size:14px;color:#475569}
.formulas{display:grid;gap:8px}
.formula{background:var(--soft);border:1px solid var(--line);border-radius:9px;padding:9px 13px;font-size:15px;overflow-x:auto}
.lp-foot{padding:16px 24px;background:var(--soft);border-top:1px solid var(--line);display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:10px}

/* Quiz */
.quiz-head{background:linear-gradient(135deg,#312e81,#1e1b4b);color:#fff;padding:30px 0 26px}
.quiz-head h1{margin:0 0 4px;font-size:28px}
.quiz-head .sub{color:#c7d2fe;font-size:15px}
.progwrap{position:sticky;top:60px;z-index:40;background:var(--soft);padding:12px 0;border-bottom:1px solid var(--line)}
.progrow{display:flex;align-items:center;gap:14px}
.progbar{flex:1;height:9px;background:var(--line);border-radius:999px;overflow:hidden}
.progbar > i{display:block;height:100%;width:0;background:linear-gradient(90deg,var(--accent),var(--brand));transition:width .3s}
.progtext{font-size:13px;color:var(--muted);white-space:nowrap;font-variant-numeric:tabular-nums}
.q{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow);padding:22px;margin:18px 0}
.q .qhead{display:flex;justify-content:space-between;gap:10px;margin-bottom:6px}
.q .qn{font-size:13px;font-weight:700;color:var(--brand)}
.q .src{font-size:12px;color:var(--muted)}
.q .stem{font-size:16.5px;margin:8px 0 16px}
.opts{display:grid;gap:10px}
.opt{display:flex;gap:12px;align-items:flex-start;border:1.5px solid var(--line);border-radius:11px;padding:12px 15px;cursor:pointer;background:#fff;transition:.12s;font-size:15.5px}
.opt:hover{border-color:var(--brand);background:#fafaff}
.opt .lab{flex:none;width:26px;height:26px;border-radius:7px;background:var(--soft);border:1px solid var(--line);display:grid;place-items:center;font-weight:700;font-size:13px;color:var(--muted)}
.opt.sel{border-color:var(--brand);background:#eef2ff}
.opt.sel .lab{background:var(--brand);color:#fff;border-color:var(--brand)}
.opt.correct{border-color:var(--ok);background:var(--okbg)}
.opt.correct .lab{background:var(--ok);color:#fff;border-color:var(--ok)}
.opt.wrong{border-color:var(--bad);background:var(--badbg)}
.opt.wrong .lab{background:var(--bad);color:#fff;border-color:var(--bad)}
.opt.locked{cursor:default}
.expl{margin-top:14px;padding:13px 15px;border-radius:10px;background:#f0f9ff;border:1px solid #bae6fd;font-size:14.5px;display:none}
.expl.show{display:block}
.expl .tag{font-weight:700;color:var(--accent);font-size:12.5px;text-transform:uppercase;letter-spacing:.03em;display:block;margin-bottom:3px}
.verdict{font-size:13px;font-weight:700;margin-bottom:8px}
.verdict.ok{color:var(--ok)}
.verdict.no{color:var(--bad)}

.quizbar{position:sticky;bottom:0;background:#fff;border-top:1px solid var(--line);padding:14px 0;box-shadow:0 -4px 16px rgba(15,23,42,.06);z-index:40}
.quizbar .container{display:flex;gap:12px;align-items:center;flex-wrap:wrap}
.quizbar .spacer{flex:1}
.btn.sm{padding:9px 16px;font-size:14px}
.btn.outline{background:#fff;color:var(--brand);border:1.5px solid var(--brand)}
.btn.outline:hover{background:#eef2ff}
.btn:disabled{opacity:.5;cursor:not-allowed;transform:none}

/* Results modal */
.scorecard{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow);padding:28px;text-align:center;margin:24px 0}
.scorecard .big{font-size:52px;font-weight:800;color:var(--brand);line-height:1}
.scorecard .pct{font-size:16px;color:var(--muted);margin-top:6px}
.ring{--p:0;width:140px;height:140px;border-radius:50%;margin:0 auto 14px;
  background:conic-gradient(var(--brand) calc(var(--p)*1%), var(--line) 0);display:grid;place-items:center}
.ring > div{width:108px;height:108px;border-radius:50%;background:#fff;display:grid;place-items:center;flex-direction:column}
.ring b{font-size:30px}
.ring span{font-size:12px;color:var(--muted)}

.footer{padding:30px 0;color:var(--muted);font-size:13px;text-align:center;border-top:1px solid var(--line);margin-top:30px}
.notice{background:#fffbeb;border:1px solid #fde68a;border-radius:11px;padding:13px 16px;font-size:14px;color:#92400e;margin:14px 0}
.empty{padding:50px;text-align:center;color:var(--muted)}
.katex{font-size:1.04em}
/* Start card / forms */
.startcard{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow);padding:26px;max-width:560px}
.startcard h3{margin:0 0 8px;font-size:20px}
.fld{display:block;margin:14px 0 8px}
.fld span{display:block;font-size:13px;font-weight:600;color:var(--muted);margin-bottom:6px}
.namehint{display:block;color:var(--bad);font-weight:600;font-style:normal;font-size:13px;margin:2px 0 8px;line-height:1.45}
.fld input{width:100%;padding:12px 14px;border:1.5px solid var(--line);border-radius:10px;font-size:16px;font-family:inherit}
.fld input:focus{outline:none;border-color:var(--brand)}
.ferr{color:var(--bad);font-size:13.5px;min-height:18px;margin:4px 0 10px}
.ferr.ok{color:var(--ok)}

/* Result / submission */
.substatus{font-size:14px;margin:14px auto 4px;max-width:520px;padding:9px 13px;border-radius:9px;background:var(--soft);border:1px solid var(--line)}
.substatus.ok{background:var(--okbg);border-color:#86efac;color:#166534}
.substatus.warn{background:#fffbeb;border-color:#fde68a;color:#92400e}
.recap{display:flex;flex-wrap:wrap;gap:6px;justify-content:center;margin:16px 0}
.chip{font-size:12px;font-weight:700;padding:3px 8px;border-radius:7px}
.chip.ok{background:var(--okbg);color:#166534}
.chip.no{background:var(--badbg);color:#991b1b}
.codecard{margin-top:18px}
.codecard h3{margin:0 0 6px;font-size:18px}
.codebox{width:100%;font-family:ui-monospace,SFMono-Regular,Menlo,monospace;font-size:12px;
  border:1.5px solid var(--line);border-radius:10px;padding:11px 13px;resize:vertical;background:var(--soft);color:#334155}

/* Toast (partial submit feedback) */
.toast{position:fixed;left:50%;bottom:78px;transform:translateX(-50%) translateY(20px);
  max-width:560px;width:calc(100% - 32px);background:#0f172a;color:#fff;border-radius:12px;
  padding:13px 18px;font-size:14px;box-shadow:0 10px 30px rgba(15,23,42,.3);opacity:0;
  pointer-events:none;transition:.25s;z-index:60}
.toast.show{opacity:1;transform:translateX(-50%) translateY(0);pointer-events:auto}
.toast.warn{background:#78350f}
.toast .codebox{color:#0f172a}
.linklike{background:none;border:none;color:#93c5fd;text-decoration:underline;cursor:pointer;font:inherit;padding:0}

/* Progress badges */
.pbadge{display:inline-block;font-size:12px;font-weight:700;padding:3px 9px;border-radius:999px}
.pbadge.done{background:var(--okbg);color:#166534}
.pbadge.wip{background:#fef3c7;color:#92400e}
.wiprow td{background:#fffdf5}

/* Teacher dashboard */
.statgrid{display:grid;grid-template-columns:repeat(auto-fit,minmax(150px,1fr));gap:14px;margin:18px 0}
.statcard{background:var(--card);border:1px solid var(--line);border-radius:12px;box-shadow:var(--shadow);padding:16px 18px;text-align:center}
.statcard b{display:block;font-size:26px;color:var(--brand)}
.statcard span{font-size:12.5px;color:var(--muted)}
.tbar{display:flex;align-items:center;gap:10px;margin-bottom:12px;flex-wrap:wrap}
.tablewrap{overflow-x:auto}
.gradetable{width:100%;border-collapse:collapse;font-size:14px}
.gradetable th{text-align:left;font-size:12px;text-transform:uppercase;letter-spacing:.03em;color:var(--muted);padding:9px 10px;border-bottom:2px solid var(--line)}
.gradetable td{padding:10px;border-bottom:1px solid var(--line);vertical-align:middle}
.gradetable tr:hover td{background:var(--soft)}
.gradetable .muted{color:var(--muted);font-size:12.5px}
.gbadge{display:inline-grid;place-items:center;min-width:26px;height:26px;padding:0 6px;border-radius:7px;font-weight:700;font-size:13px;color:#fff}
.gbadge.gA{background:#16a34a}.gbadge.gB{background:#0ea5e9}.gbadge.gC{background:#d97706}.gbadge.gD{background:#f97316}.gbadge.gF{background:#dc2626}
.tbtn{border:1px solid var(--line);background:#fff;border-radius:8px;padding:5px 11px;font-size:13px;font-weight:600;color:var(--brand);cursor:pointer;margin-left:5px}
.tbtn:hover{background:#eef2ff}
.tbtn.del{color:var(--bad)}
.tbtn.del:hover{background:var(--badbg)}
.btn.danger{color:var(--bad);border-color:#fecaca}
.btn.danger:hover{background:var(--badbg)}
.detaillist{display:flex;flex-direction:column;gap:14px;margin-top:8px}
.dq{border:1px solid var(--line);border-left:4px solid var(--line);border-radius:10px;padding:14px 16px;background:#fff}
.dq.okrow{border-left-color:var(--ok)}
.dq.norow{border-left-color:var(--bad)}
.dqhead{display:flex;justify-content:space-between;gap:10px;font-size:13px;margin-bottom:6px}
.vok{color:var(--ok);font-weight:700}.vno{color:var(--bad);font-weight:700}
.opts.mini{gap:7px;margin-top:8px}
.opts.mini .opt{padding:8px 12px;font-size:14px;cursor:default}
.pickedtag{color:var(--brand);font-style:normal;font-weight:700;font-size:12px}
code{background:var(--soft);padding:1px 6px;border-radius:5px;font-size:13px}

/* Analytics */
.anselect{display:flex;align-items:center;gap:8px;font-size:13px;font-weight:600;color:var(--muted)}
.anselect select{padding:7px 10px;border:1.5px solid var(--line);border-radius:9px;font-size:14px;font-family:inherit;background:#fff;color:var(--ink)}
.anh{font-size:15px;text-transform:uppercase;letter-spacing:.03em;color:var(--brand2);margin:22px 0 4px}
.anlead{margin:0 0 12px;font-size:13px}
.accpill{display:inline-block;min-width:46px;text-align:center;font-weight:700;font-size:13px;padding:3px 9px;border-radius:999px}
.accpill.acc-hi{background:var(--okbg);color:#166534}
.accpill.acc-mid{background:#fef3c7;color:#92400e}
.accpill.acc-lo{background:var(--badbg);color:#991b1b}
.rankcell{font-size:16px;font-weight:700}
.diffstem{font-size:12.5px;color:var(--muted);max-width:380px;margin-top:3px;
  display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden}
.wrongcell{font-size:13px;max-width:260px;
  display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden}
.diffstem .katex,.wrongcell .katex{font-size:1em}
#diffTable td{vertical-align:top}

@media (max-width:640px){
  .hero h1{font-size:30px}
  .topbar .container{height:auto;min-height:52px;flex-wrap:wrap;gap:6px 10px;padding-top:8px;padding-bottom:8px}
  .brand{font-size:16px;width:100%}
  .nav{margin-left:0;width:100%;gap:4px}
  .nav a{padding:6px 11px;font-size:13px}
  .topbar{position:static}
  .progwrap{top:0}
  .hero{padding:34px 0 38px}
  .quizbar .container{gap:8px}
  .btn.sm{padding:8px 12px;font-size:13px}
}