:root{
  --ink:#111111;
  --ink-2:#555555;
  --ink-3:#9a9a9a;
  --line:#e4e4e0;
  --line-strong:#c9c9c4;
  --bg:#ffffff;
  --bg-soft:#f7f7f5;
  --answered:#3B82F6;
  --correct:#22C55E;
  --wrong:#EF4444;
  --nokey:#9CA3AF;
  --radius:6px;
}
*{margin:0;padding:0;box-sizing:border-box;}
html,body{height:100%;}
body{
  font-family:-apple-system,BlinkMacSystemFont,"PingFang SC","Hiragino Sans GB","Microsoft YaHei","Segoe UI",sans-serif;
  color:var(--ink);background:var(--bg);
  font-size:14px;line-height:1.6;
  -webkit-font-smoothing:antialiased;
}
button{font-family:inherit;cursor:pointer;}

/* ---------- 顶栏 ---------- */
.topbar{
  height:52px;border-bottom:1px solid var(--line);
  display:flex;align-items:center;justify-content:space-between;
  padding:0 20px;position:sticky;top:0;background:var(--bg);z-index:20;
}
.topbar .title{font-size:15px;font-weight:600;letter-spacing:.02em;}

/* ---------- 移动端标签 ---------- */
.mobile-tabs{display:none;}

/* ---------- 三栏布局 ---------- */
.layout{
  display:grid;
  grid-template-columns:280px 1fr 320px;
  height:calc(100vh - 52px);
}
.col{overflow-y:auto;height:100%;}
.col-left{border-right:1px solid var(--line);background:var(--bg);}
.col-center{display:flex;flex-direction:column;}
.col-right{border-left:1px solid var(--line);background:var(--bg);display:flex;flex-direction:column;}

.col-head{
  padding:14px 16px 10px;font-size:12px;color:var(--ink-3);
  letter-spacing:.12em;border-bottom:1px solid var(--line);
  position:sticky;top:0;background:inherit;z-index:5;
}

/* ---------- 左栏：试卷列表 ---------- */
.paper-list{padding:8px 0 24px;}
.paper-item{
  position:relative;padding:12px 44px 12px 16px;cursor:pointer;
  border-bottom:1px solid var(--line);
  transition:background .12s;
}
.paper-item:hover{background:var(--bg-soft);}
.paper-item.active{background:var(--bg-soft);box-shadow:inset 2px 0 0 var(--ink);}
.paper-name{font-size:13px;line-height:1.55;font-weight:500;}
.paper-item.active .paper-name{font-weight:600;}
.paper-meta{margin-top:6px;display:flex;align-items:center;gap:8px;}
.tag{
  font-size:11px;padding:1px 7px;border-radius:99px;border:1px solid var(--line-strong);
  color:var(--ink-2);line-height:1.6;
}
.tag.set{color:var(--ink);border-color:var(--ink);}
.tag.graded{color:#166534;border-color:#bbf7d0;background:#f0fdf4;}
.paper-progress{font-size:11px;color:var(--ink-3);font-variant-numeric:tabular-nums;}

/* ---------- 中栏：答题区 ---------- */
.q-wrap{flex:1;display:flex;flex-direction:column;padding:28px 36px;max-width:720px;width:100%;margin:0 auto;}
.q-progress{font-size:12px;color:var(--ink-3);letter-spacing:.08em;font-variant-numeric:tabular-nums;}
.q-number{font-size:34px;font-weight:650;margin-top:6px;letter-spacing:.01em;}
.q-tip{font-size:13px;color:var(--ink-3);margin-top:4px;}
.q-divider{border:none;border-top:1px solid var(--line);margin:22px 0;}

.options{display:flex;flex-direction:column;gap:10px;}
.opt{
  display:flex;align-items:center;gap:14px;
  border:1px solid var(--line-strong);border-radius:var(--radius);
  background:var(--bg);padding:14px 18px;text-align:left;
  font-size:15px;transition:border-color .12s,background .12s;
}
.opt:hover:not(:disabled){border-color:var(--ink);}
.opt .letter{
  width:30px;height:30px;border:1px solid var(--line-strong);border-radius:50%;
  display:flex;align-items:center;justify-content:center;
  font-size:14px;font-weight:600;flex:none;font-variant-numeric:tabular-nums;
  transition:all .12s;
}
.opt.selected{border-color:var(--answered);background:#eff6ff;}
.opt.selected .letter{background:var(--answered);border-color:var(--answered);color:#fff;}
.opt:disabled{cursor:default;}
.opt.grade-correct{border-color:var(--correct);background:#f0fdf4;}
.opt.grade-correct .letter{background:var(--correct);border-color:var(--correct);color:#fff;}
.opt.grade-wrong{border-color:var(--wrong);background:#fef2f2;}
.opt.grade-wrong .letter{background:var(--wrong);border-color:var(--wrong);color:#fff;}
.opt .mark{margin-left:auto;font-size:12px;color:var(--ink-3);}
.opt.multi .letter{border-radius:6px;}
.q-badge{
  display:inline-block;font-size:11px;color:var(--ink-2);border:1px solid var(--line-strong);
  border-radius:99px;padding:1px 10px;margin-left:10px;vertical-align:middle;font-weight:400;
}

.grade-summary{
  margin-top:20px;border:1px solid var(--line);border-radius:var(--radius);
  padding:12px 16px;font-size:13px;background:var(--bg-soft);
  display:flex;gap:18px;flex-wrap:wrap;font-variant-numeric:tabular-nums;
}
.grade-summary b{font-weight:600;}
.verdict{font-weight:600;}
.verdict.ok{color:#15803d;}
.verdict.bad{color:#b91c1c;}
.verdict.none{color:var(--ink-3);}

.q-nav{display:flex;gap:10px;margin-top:auto;padding-top:28px;}
.btn{
  border:1px solid var(--line-strong);background:var(--bg);color:var(--ink);
  padding:9px 20px;border-radius:var(--radius);font-size:13px;
  transition:all .12s;
}
.btn:hover:not(:disabled){border-color:var(--ink);}
.btn:disabled{color:var(--ink-3);border-color:var(--line);cursor:not-allowed;background:var(--bg-soft);}
.btn-primary{background:var(--ink);color:#fff;border-color:var(--ink);}
.btn-primary:hover:not(:disabled){background:#000;border-color:#000;}
.kbd-hint{font-size:11px;color:var(--ink-3);margin-top:14px;}
kbd{
  font-family:inherit;font-size:10px;border:1px solid var(--line-strong);
  border-bottom-width:2px;border-radius:4px;padding:0 5px;color:var(--ink-2);
}

/* ---------- 右栏：答题卡 ---------- */
.card-stats{
  padding:14px 18px;border-bottom:1px solid var(--line);
  display:flex;align-items:baseline;justify-content:space-between;
}
.card-stats .num{font-size:20px;font-weight:650;font-variant-numeric:tabular-nums;}
.card-stats .label{font-size:12px;color:var(--ink-3);}
.legend{display:flex;gap:12px;padding:10px 18px;border-bottom:1px solid var(--line);flex-wrap:wrap;}
.legend span{display:flex;align-items:center;gap:5px;font-size:11px;color:var(--ink-2);}
.legend i{width:10px;height:10px;border-radius:2px;display:inline-block;border:1px solid var(--line-strong);}
.legend .l-answered i{background:var(--answered);border-color:var(--answered);}
.legend .l-correct i{background:var(--correct);border-color:var(--correct);}
.legend .l-wrong i{background:var(--wrong);border-color:var(--wrong);}
.legend .l-nokey i{background:var(--nokey);border-color:var(--nokey);}

.grid-wrap{flex:1;overflow-y:auto;padding:16px 18px;}
.card-grid{
  display:grid;grid-template-columns:repeat(10,1fr);gap:5px;
}
.cell{
  aspect-ratio:1;border:1px solid var(--line-strong);border-radius:4px;
  background:var(--bg);font-size:11px;color:var(--ink-2);
  display:flex;align-items:center;justify-content:center;
  font-variant-numeric:tabular-nums;transition:all .1s;padding:0;
}
.cell:hover{border-color:var(--ink);color:var(--ink);}
.cell.current{outline:2px solid var(--ink);outline-offset:1px;color:var(--ink);font-weight:600;}
.cell.answered{background:var(--answered);border-color:var(--answered);color:#fff;}
.cell.correct{background:var(--correct);border-color:var(--correct);color:#fff;}
.cell.wrong{background:var(--wrong);border-color:var(--wrong);color:#fff;}
.cell.nokey{background:var(--nokey);border-color:var(--nokey);color:#fff;}

.card-foot{padding:16px 18px;border-top:1px solid var(--line);}
.card-foot .btn{width:100%;padding:11px;font-size:14px;}
.score-line{
  text-align:center;font-size:13px;color:var(--ink-2);margin-bottom:12px;
  font-variant-numeric:tabular-nums;
}
.score-line b{font-size:22px;font-weight:650;color:var(--ink);}
.card-foot .row{display:flex;gap:10px;}
.card-foot .row .btn{flex:1;}

/* ---------- 弹窗 ---------- */
.overlay{
  position:fixed;inset:0;background:rgba(17,17,17,.35);z-index:100;
  display:none;align-items:center;justify-content:center;padding:20px;
}
.overlay.open{display:flex;}
.modal{
  background:var(--bg);border-radius:10px;width:100%;max-width:480px;
  max-height:86vh;display:flex;flex-direction:column;
  box-shadow:0 24px 64px rgba(0,0,0,.18);
}
.modal-head{padding:18px 22px 14px;border-bottom:1px solid var(--line);}
.modal-head h3{font-size:15px;font-weight:600;line-height:1.5;}
.modal-head p{font-size:12px;color:var(--ink-3);margin-top:4px;}
.modal-body{padding:18px 22px;overflow-y:auto;}
.modal-foot{
  padding:14px 22px;border-top:1px solid var(--line);
  display:flex;justify-content:flex-end;gap:10px;
}
.confirm-text{font-size:14px;line-height:1.8;}

/* ---------- Toast ---------- */
.toast{
  position:fixed;left:50%;bottom:36px;transform:translateX(-50%) translateY(16px);
  background:var(--ink);color:#fff;font-size:13px;padding:10px 20px;
  border-radius:99px;opacity:0;pointer-events:none;transition:all .25s;z-index:200;
  max-width:88vw;text-align:center;
}
.toast.show{opacity:1;transform:translateX(-50%) translateY(0);}

/* ---------- 响应式 ---------- */
@media (max-width:1080px){
  .layout{grid-template-columns:240px 1fr 280px;}
}
@media (max-width:900px){
  .layout{grid-template-columns:1fr;height:calc(100vh - 52px - 46px);}
  .col{display:none;border:none;}
  .col.show{display:flex;flex-direction:column;}
  .col-center.show{display:flex;}
  .mobile-tabs{
    display:flex;border-bottom:1px solid var(--line);background:var(--bg);
    position:sticky;top:52px;z-index:20;
  }
  .mobile-tabs button{
    flex:1;border:none;background:none;padding:12px;font-size:13px;color:var(--ink-3);
    border-bottom:2px solid transparent;
  }
  .mobile-tabs button.on{color:var(--ink);font-weight:600;border-bottom-color:var(--ink);}
  .q-wrap{padding:20px 20px;}
  .card-grid{grid-template-columns:repeat(10,1fr);}
}
@media (max-width:520px){
  .card-grid{grid-template-columns:repeat(8,1fr);}
}