:root {
  --bg: #fafafa;
  --fg: #1f1f1f;
  --muted: #666;
  --accent: #b8001f;
  --border: #d8d8d8;
  --row-alt: #f3f3f3;
  --header-bg: #1f1f1f;
  --header-fg: #fff;
  --detail-bg: #fffbe6;
  --card-bg: #fff;
  --tag-millennium: #b8001f;
  --tag-number: #1565c0;
  --tag-geom: #2e7d32;
  --tag-pde: #6a1b9a;
  --tag-cs: #ef6c00;
  --tag-comb: #00838f;
  --tag-other: #455a64;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  padding: 2.5rem 1.5rem;
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "PingFang SC",
               "Helvetica Neue", Helvetica, "Microsoft YaHei", sans-serif;
  background: var(--bg);
  color: var(--fg);
  line-height: 1.55;
}
.container { max-width: 1400px; margin: 0 auto; }
h1 { margin: 0 0 .5rem; font-size: 1.9rem; letter-spacing: .02em; }
.subtitle { color: var(--muted); margin: 0 0 1.5rem; font-size: .95rem; }
.crumbs { font-size: .85rem; color: var(--muted); margin: 0 0 1rem; }
.crumbs a { color: var(--tag-number); text-decoration: none; }
.crumbs a:hover { text-decoration: underline; }
.toolbar {
  display: flex; flex-wrap: wrap; gap: .6rem; align-items: center; margin: 0 0 1rem;
}
.toolbar button {
  font: inherit; font-size: .85rem; padding: .4rem .85rem;
  border: 1px solid var(--border); background: #fff; border-radius: 6px;
  cursor: pointer; color: var(--fg);
}
.toolbar button:hover { background: #f0f0f0; }
.toolbar input[type="text"] {
  font: inherit; font-size: .85rem; padding: .4rem .7rem;
  border: 1px solid var(--border); border-radius: 6px;
  background: #fff; min-width: 220px;
}
.legend {
  margin: 0 0 1.25rem; display: flex; flex-wrap: wrap; gap: .5rem; font-size: .82rem;
}
.tag {
  display: inline-block; padding: 2px 8px; border-radius: 10px;
  color: #fff; font-size: .75rem; white-space: nowrap;
}
.tag.millennium { background: var(--tag-millennium); }
.tag.number     { background: var(--tag-number); }
.tag.geom       { background: var(--tag-geom); }
.tag.pde        { background: var(--tag-pde); }
.tag.cs         { background: var(--tag-cs); }
.tag.comb       { background: var(--tag-comb); }
.tag.other      { background: var(--tag-other); }

.cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1rem;
  margin: 1.5rem 0;
}
.card {
  background: var(--card-bg); border: 1px solid var(--border);
  border-radius: 10px; padding: 1.1rem 1.2rem; text-decoration: none;
  color: var(--fg); transition: transform .15s ease, box-shadow .15s ease;
  display: block;
}
.card:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 16px rgba(0,0,0,.08);
}
.card h3 { margin: 0 0 .35rem; font-size: 1.05rem; }
.card .count { color: var(--accent); font-weight: 600; font-size: .9rem; }
.card p { margin: .35rem 0 0; color: var(--muted); font-size: .85rem; }

.table-wrap {
  overflow-x: auto; border: 1px solid var(--border); border-radius: 10px;
  background: #fff; box-shadow: 0 1px 3px rgba(0,0,0,.04);
}
table {
  width: 100%; border-collapse: collapse; font-size: .9rem; min-width: 1100px;
}
thead th {
  background: var(--header-bg); color: var(--header-fg);
  text-align: left; padding: .7rem .8rem; font-weight: 600;
  position: sticky; top: 0; z-index: 2; white-space: nowrap;
}
tbody td {
  padding: .65rem .85rem; border-top: 1px solid var(--border); vertical-align: top;
}
tr.summary { cursor: pointer; transition: background .15s ease; }
tr.summary:nth-child(4n+1) { background: var(--row-alt); }
tr.summary:hover { background: #fff3cd; }
tr.summary.open { background: #ffe9a8; }

.chevron {
  display: inline-block; width: 1em; transition: transform .2s ease;
  color: var(--muted); margin-right: .35rem;
}
tr.summary.open .chevron { transform: rotate(90deg); color: var(--accent); }

.name { font-weight: 600; }
.difficulty, .attention { color: var(--accent); letter-spacing: 1px; white-space: nowrap; }
.attention.high   { color: #b8001f; }
.attention.mid    { color: #ef6c00; }
.attention.low    { color: #999; }
.prize-cash       { color: var(--tag-millennium); font-weight: 600; }
.prize-none       { color: var(--muted); }
.status           { font-size: .86rem; }

tr.detail { display: none; background: var(--detail-bg); }
tr.detail.open { display: table-row; }
tr.detail td {
  padding: 1rem 1.5rem 1.2rem;
  border-top: 1px dashed #d6c98a;
  border-bottom: 2px solid #e6d27a;
}
.detail-body { font-size: .92rem; color: #2a2a2a; line-height: 1.7; }
.detail-body h3 { margin: 0 0 .55rem; font-size: 1.02rem; color: var(--accent); }
.detail-body p { margin: .35rem 0; }
.detail-body .formula {
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  background: #fff; border: 1px solid #e6d27a; border-radius: 4px;
  padding: .5rem .7rem; margin: .5rem 0; display: inline-block; font-size: .9rem;
}
.detail-body ul { margin: .35rem 0 .35rem 1.2rem; padding: 0; }
.detail-body li { margin: .2rem 0; }
.detail-body .label {
  display: inline-block; min-width: 5.5em;
  color: #8a6500; font-weight: 600;
}

.footer {
  margin-top: 2rem; padding: 1.2rem 1.4rem;
  background: #fff; border: 1px solid var(--border); border-radius: 10px;
  font-size: .9rem; color: #333;
}
.footer h2 { font-size: 1.05rem; margin: 0 0 .6rem; color: var(--accent); }
.footer ul { margin: .3rem 0 0; padding-left: 1.3rem; }
.footer li { margin: .25rem 0; }
.meta { margin-top: 1.2rem; font-size: .8rem; color: var(--muted); text-align: right; }

tr.hidden-search { display: none !important; }

/* KaTeX tweaks */
.katex { font-size: 1em; }
.detail-body .katex-display { margin: .5rem 0; }
.detail-body .katex-display > .katex {
  background: #fff;
  border: 1px solid #e6d27a;
  border-radius: 4px;
  padding: .5rem .8rem;
  display: inline-block;
}
.status .katex, .name .katex { font-size: .95em; }

/* Disproved marker */
.tag.disproved {
  background: #6a1b9a;
  background: linear-gradient(90deg, #b8001f 0%, #6a1b9a 100%);
  font-weight: 700;
}
tr.summary.disproved td { background: #fbeef1 !important; }
tr.summary.disproved .name { text-decoration: line-through; text-decoration-color: #b8001f; text-decoration-thickness: 1px; }
tr.summary.disproved:hover td { background: #f7d7df !important; }
.detail-body .disproved-banner {
  background: #fbeef1;
  border-left: 4px solid #b8001f;
  padding: .55rem .8rem;
  margin: 0 0 .6rem;
  font-weight: 600;
  color: #b8001f;
}
.detail-body .disproved-banner a {
  color: #6a1b9a;
  text-decoration: underline;
}

/* Language toggle */
.lang-toggle {
  display: inline-flex;
  border: 1px solid var(--border);
  border-radius: 6px;
  overflow: hidden;
  background: #fff;
  margin-left: auto;
}
.lang-toggle button {
  font: inherit;
  font-size: .78rem;
  letter-spacing: .05em;
  padding: .35rem .7rem;
  border: 0;
  background: transparent;
  color: var(--muted);
  cursor: pointer;
  border-right: 1px solid var(--border);
  min-width: 2.4rem;
}
.lang-toggle button:last-child { border-right: 0; }
.lang-toggle button.active {
  background: var(--header-bg);
  color: #fff;
}
.lang-toggle button:hover:not(.active) { background: #f0f0f0; color: var(--fg); }

/* Bilingual detail bodies: show one block at a time */
html[lang^="zh"] .detail-body .lang-en { display: none; }
html[lang^="en"] .detail-body .lang-zh { display: none; }
.detail-body .lang-zh, .detail-body .lang-en { display: block; }