:root {
  --bg: #f6f7f9;
  --card: #ffffff;
  --ink: #1b1f24;
  --muted: #6b7280;
  --line: #e5e7eb;
  --brand: #1d4ed8;
  --ok: #0f7b3f;
  --bad: #b42318;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.65 -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
}

.top {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: center;
  justify-content: space-between;
  padding: 14px 18px;
  background: #fff;
  border-bottom: 1px solid var(--line);
  position: sticky;
  top: 0;
  z-index: 10;
}

.brand { display: flex; gap: 10px; align-items: center; }

.logo {
  width: 34px;
  height: 34px;
  border-radius: 9px;
  background: var(--brand);
  color: #fff;
  display: grid;
  place-items: center;
  font-weight: 700;
}

.top h1 { font-size: 17px; margin: 0; }
.sub { margin: 2px 0 0; color: var(--muted); font-size: 12px; }

.tabs { display: flex; gap: 6px; }
.tabs button {
  border: 1px solid var(--line);
  background: #fff;
  padding: 6px 14px;
  border-radius: 999px;
  font-size: 14px;
  cursor: pointer;
  color: var(--muted);
}
.tabs button.on { background: var(--brand); border-color: var(--brand); color: #fff; }

.badge {
  display: inline-block;
  min-width: 18px;
  margin-left: 4px;
  background: #fee4e2;
  color: var(--bad);
  border-radius: 999px;
  font-size: 11px;
  padding: 0 5px;
}

main { max-width: 860px; margin: 0 auto; padding: 18px; }

.filters {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
  margin-bottom: 14px;
}

label { font-size: 13px; color: var(--muted); display: flex; gap: 6px; align-items: center; }

select, input[type="search"] {
  padding: 6px 10px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  font-size: 14px;
  color: var(--ink);
}

input[type="search"] { flex: 1; min-width: 180px; }

button {
  padding: 7px 14px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  color: var(--ink);
  font-size: 14px;
  cursor: pointer;
}
button:hover { border-color: #c7cbd1; }
button.primary { background: var(--brand); border-color: var(--brand); color: #fff; }

.bar-wrap { margin: 4px 0 14px; }
.bar { height: 6px; background: #e8eaee; border-radius: 999px; overflow: hidden; }
.bar i { display: block; height: 100%; width: 0; background: var(--brand); transition: width .2s; }
.bar-meta {
  display: flex;
  justify-content: space-between;
  font-size: 12px;
  color: var(--muted);
  margin-top: 6px;
}

.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 20px;
}

.tags { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 12px; }
.tag {
  font-size: 12px;
  padding: 2px 9px;
  border-radius: 999px;
  background: #eef2ff;
  color: #3441b5;
}
.tag.diff { background: #fff7e6; color: #92580d; }
.tag.freq { background: #e8f7ee; color: #0f7b3f; }
.tag.src { background: #f2f3f5; color: var(--muted); }

.stem { font-size: 16px; white-space: pre-wrap; margin: 0 0 16px; }

.options { display: grid; gap: 9px; }

.opt {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  text-align: left;
  padding: 11px 13px;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: #fff;
  font-size: 15px;
  cursor: pointer;
  line-height: 1.5;
}
.opt:hover:not(.done) { border-color: #b9c0cc; background: #fbfcfe; }
.opt .k {
  flex: 0 0 22px;
  height: 22px;
  border-radius: 50%;
  background: #f1f3f7;
  display: grid;
  place-items: center;
  font-size: 12px;
  color: #4b5563;
}
.opt.right { border-color: var(--ok); background: #effaf3; }
.opt.right .k { background: var(--ok); color: #fff; }
.opt.wrong { border-color: var(--bad); background: #fef3f2; }
.opt.wrong .k { background: var(--bad); color: #fff; }

.feedback { margin-top: 16px; border-top: 1px dashed var(--line); padding-top: 14px; }
.fb-answer { font-weight: 700; margin: 0 0 10px; }
.fb-answer.ok { color: var(--ok); }
.fb-answer.bad { color: var(--bad); }
.fb-block { margin: 0 0 12px; }
.fb-block h3 {
  font-size: 12px;
  letter-spacing: .08em;
  color: var(--muted);
  margin: 0 0 5px;
}
.fb-block p { margin: 0; white-space: pre-wrap; font-size: 15px; }
.fb-block.essence p { background: #f7f9ff; border-radius: 8px; padding: 10px 12px; }

.actions { display: flex; gap: 8px; align-items: center; margin-top: 18px; flex-wrap: wrap; }
.hint { font-size: 12px; color: var(--muted); margin-left: auto; }

.count { font-size: 13px; color: var(--muted); }
.list { display: grid; gap: 8px; }
.row {
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 12px 14px;
  cursor: pointer;
  font-size: 14px;
  display: flex;
  gap: 10px;
  align-items: flex-start;
}
.row:hover { border-color: #b9c0cc; }
.row .n { color: var(--muted); font-size: 12px; min-width: 34px; }
.row .s { flex: 1; }

.foot {
  max-width: 860px;
  margin: 0 auto;
  padding: 20px 18px 40px;
  display: flex;
  gap: 10px;
  justify-content: space-between;
  color: var(--muted);
  font-size: 12px;
}

@media (max-width: 620px) {
  .top { padding: 10px 12px; }
  .top h1 { font-size: 15px; }
  main { padding: 12px; }
  .card { padding: 15px; border-radius: 12px; }
  .hint { display: none; }
  .tabs button { padding: 6px 10px; font-size: 13px; }
}