:root {
  --fg: #1a1a1a;
  --muted: #666;
  --bg: #fff;
  --accent: #0b5fa3;
  --accent-bg: #e8f1fa;
  --border: #d8d8d8;
  --code-bg: #f4f4f4;
  --erdos: #6e3aa6;
  --warn: #b14d00;
  --ok: #1f7a3a;
}

* { box-sizing: border-box; }

html { font-size: 16px; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", Arial, sans-serif;
  color: var(--fg);
  background: var(--bg);
  line-height: 1.5;
}

main {
  max-width: 1100px;
  margin: 0 auto;
  padding: 1.25rem 1.5rem 3rem;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.site-header {
  border-bottom: 1px solid var(--border);
  padding: 0.75rem 1.5rem;
  display: flex;
  align-items: baseline;
  gap: 1.5rem;
  max-width: 1100px;
  margin: 0 auto;
}
.site-title {
  font-weight: 600;
  font-size: 1.05rem;
  color: var(--fg);
}
.site-header nav { display: flex; gap: 1rem; font-size: 0.95rem; }
.site-footer {
  border-top: 1px solid var(--border);
  margin-top: 3rem;
  padding: 1rem 1.5rem;
  font-size: 0.85rem;
  color: var(--muted);
  max-width: 1100px;
  margin: 3rem auto 0;
}

/* ---------- index ---------- */

.index-controls {
  display: flex;
  align-items: center;
  gap: 1rem;
  margin: 1rem 0;
}
.index-controls input[type=search] {
  flex: 1;
  padding: 0.5rem 0.75rem;
  font-size: 1rem;
  border: 1px solid var(--border);
  border-radius: 4px;
}
.index-count { color: var(--muted); font-size: 0.9rem; white-space: nowrap; }

table.problems-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.93rem;
}
table.problems-table th,
table.problems-table td {
  text-align: left;
  padding: 0.4rem 0.6rem;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}
table.problems-table th {
  font-weight: 600;
  background: var(--code-bg);
  position: sticky;
  top: 0;
  user-select: none;
}
table.problems-table th.sorted-asc::after  { content: ' ▲'; font-size: 0.7em; color: var(--muted); }
table.problems-table th.sorted-desc::after { content: ' ▼'; font-size: 0.7em; color: var(--muted); }
.col-title { width: 26%; }
.col-source { width: 6%; white-space: nowrap; }
.col-status { width: 8%; white-space: nowrap; }
.col-subject { width: 18%; }
.col-authors { width: 18%; }
.col-importance { width: 6%; white-space: nowrap; }
.col-posted { width: 10%; white-space: nowrap; color: var(--muted); }

.source-summary {
  display: inline-flex;
  gap: 0.35rem;
  align-items: center;
  margin-left: 0.5rem;
  font-size: 0.85rem;
}
.source-summary .badge.source { cursor: pointer; }
.source-summary .badge.source.active { outline: 2px solid var(--accent); }

.badge.source {
  font-size: 0.7rem;
  padding: 0.05rem 0.4rem;
  border-radius: 3px;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  font-weight: 600;
}
.badge.source-opg   { background: var(--accent-bg); color: var(--accent); }
.badge.source-arxiv { background: #fff3e0;          color: #b85c00;       }
.badge.pdf-source   { background: #ececec;          color: #555;           font-size: 0.7rem; padding: 0.05rem 0.35rem; border-radius: 3px; }

.status-summary {
  display: inline-flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  align-items: center;
  font-size: 0.85rem;
}
.status-pending { color: var(--muted); }

.status-badge {
  display: inline-block;
  font-size: 0.72rem;
  padding: 0.05rem 0.45rem;
  border-radius: 3px;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  font-weight: 600;
  vertical-align: 0.1em;
  white-space: nowrap;
}
.status-open      { background: #fff4d6; color: #8a6300; }
.status-partial   { background: #fce8d4; color: #b14d00; }
.status-solved    { background: #d8efe1; color: #1f7a3a; }
.status-disproved { background: #fadbd8; color: #b03030; }
.status-unclear   { background: #ececec; color: #555; }

/* literature-review section on problem detail */
section.lit-review {
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 0.8rem 1rem;
  background: #fafbfc;
  margin: 1rem 0 1.5rem;
}
section.lit-review h2 {
  margin: 0 0 0.5rem;
  font-size: 1.05rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex-wrap: wrap;
}
section.lit-review h3 {
  font-size: 0.95rem;
  margin: 1rem 0 0.4rem;
  color: var(--muted);
}
section.lit-review .summary { margin: 0.4rem 0 0.8rem; }
section.lit-review .confidence {
  font-size: 0.78rem;
  font-weight: 400;
  color: var(--muted);
  text-transform: lowercase;
  letter-spacing: 0;
}
section.lit-review .confidence-low { color: var(--warn); }

ul.since-posted {
  list-style: none;
  padding: 0;
  margin: 0;
}
ul.since-posted > li {
  margin: 0.6rem 0;
  padding: 0.4rem 0 0.4rem 0.6rem;
  border-left: 2px solid var(--border);
}
.ref-line { display: flex; gap: 0.4rem; align-items: baseline; flex-wrap: wrap; }
.ref-title a { color: var(--fg); }
.ref-title a:hover { color: var(--accent); }
.ref-year { color: var(--muted); font-size: 0.9rem; }
.ref-meta { font-size: 0.85rem; color: var(--muted); margin-top: 0.1rem; }
.ref-claim { font-size: 0.92rem; margin: 0.3rem 0 0; }

.ref-kind {
  display: inline-block;
  font-size: 0.7rem;
  padding: 0.02rem 0.35rem;
  border-radius: 3px;
  text-transform: uppercase;
  font-weight: 600;
  letter-spacing: 0.03em;
  background: var(--code-bg);
  color: var(--muted);
}
.kind-proof          { background: #d8efe1; color: #1f7a3a; }
.kind-counterexample { background: #fadbd8; color: #b03030; }
.kind-partial        { background: #fce8d4; color: #b14d00; }
.kind-survey         { background: #e8f1fa; color: var(--accent); }
.kind-reduction      { background: #f1e9fb; color: var(--erdos); }

section.lit-review .notes {
  font-size: 0.88rem;
  color: var(--muted);
  margin-top: 0.8rem;
}
section.lit-review .review-meta {
  font-size: 0.78rem;
  color: var(--muted);
  margin-top: 0.8rem;
  border-top: 1px solid var(--border);
  padding-top: 0.4rem;
}

.importance-outstanding { color: #b14d00; font-weight: 600; }
.importance-high { color: #c08400; }
.importance-medium { color: var(--muted); }
.importance-low { color: #999; }

/* arxiv-detail subtitle: paper-internal label + arxiv id under the nice name */
.paper-label {
  margin: -0.4rem 0 0.6rem;
  font-size: 0.88rem;
  color: var(--muted);
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
}

/* ---------- timeline ---------- */

.timeline-page {
  margin-top: 1rem;
}
.timeline-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
  margin: 1rem 0 1.2rem;
}
.timeline-header h1 {
  font-size: 1.55rem;
  line-height: 1.2;
  margin: 0 0 0.35rem;
}
.timeline-header p {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}
.timeline-actions {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 0.35rem;
}
.timeline-filter-group {
  display: inline-flex;
  gap: 0.35rem;
  flex-wrap: wrap;
  justify-content: flex-end;
}
.timeline-filter {
  border: 1px solid var(--border);
  border-radius: 4px;
  background: #fff;
  color: var(--fg);
  font: inherit;
  font-size: 0.86rem;
  padding: 0.35rem 0.55rem;
  cursor: pointer;
}
.timeline-filter:hover,
.timeline-filter.active {
  border-color: var(--accent);
  background: var(--accent-bg);
  color: var(--accent);
}
.timeline-shell {
  width: 100%;
}
.timeline-axis,
.timeline-row {
  display: grid;
  grid-template-columns: minmax(12rem, 30%) minmax(18rem, 1fr) minmax(12rem, 18%);
  gap: 0.8rem;
  align-items: center;
}
.timeline-axis {
  color: var(--muted);
  font-size: 0.78rem;
  padding: 0 0 0.5rem;
}
.timeline-axis-track {
  position: relative;
  height: 1.4rem;
  border-bottom: 1px solid var(--border);
}
.timeline-tick {
  position: absolute;
  bottom: -0.1rem;
  transform: translateX(-50%);
  white-space: nowrap;
}
.timeline-tick::before {
  content: "";
  display: block;
  width: 1px;
  height: 0.45rem;
  margin: 0 auto 0.15rem;
  background: var(--border);
}
.timeline-list {
  border-top: 1px solid var(--border);
}
.timeline-row {
  min-height: 2.35rem;
  padding: 0.35rem 0;
  border-bottom: 1px solid var(--border);
}
.timeline-name {
  display: block;
  min-width: 0;
}
.timeline-name > span:first-child {
  display: block;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.timeline-subtitle {
  display: block;
  margin-top: 0.05rem;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  color: var(--muted);
  font-size: 0.78rem;
}
.timeline-track {
  position: relative;
  height: 0.8rem;
  background: linear-gradient(to right, transparent 0, transparent calc(100% - 1px), var(--border) calc(100% - 1px));
}
.timeline-track::before {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  top: 50%;
  border-top: 1px solid #e6e6e6;
}
.timeline-bar {
  position: absolute;
  top: 50%;
  display: block;
  min-width: 0.45rem;
  height: 0.45rem;
  transform: translateY(-50%);
  border-radius: 999px;
}
.timeline-bar::before,
.timeline-bar::after {
  content: "";
  position: absolute;
  top: 50%;
  width: 0.5rem;
  height: 0.5rem;
  border-radius: 50%;
  background: inherit;
  transform: translate(-50%, -50%);
}
.timeline-bar::before { left: 0; }
.timeline-bar::after { left: 100%; }
.timeline-solved { background: var(--ok); }
.timeline-disproved { background: #b03030; }
.timeline-years {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 0.35rem;
  color: var(--muted);
  font-size: 0.82rem;
  white-space: nowrap;
}
.timeline-arrow,
.timeline-duration {
  color: #888;
}
.timeline-note {
  color: var(--muted);
  font-size: 0.86rem;
  margin-top: 0.9rem;
}

/* ---------- problem detail ---------- */

article.problem header h1 {
  margin: 0 0 0.5rem;
  font-size: 1.6rem;
  line-height: 1.2;
}
article.problem .meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem 1rem;
  font-size: 0.9rem;
  color: var(--muted);
  margin-bottom: 0.4rem;
}
article.problem .importance {
  font-weight: 500;
}
article.problem .byline {
  font-size: 0.92rem;
  color: var(--muted);
  margin-bottom: 1.2rem;
}
article.problem .byline strong { color: var(--fg); }

.intersection {
  background: var(--accent-bg);
  border-left: 3px solid var(--accent);
  padding: 0.6rem 0.9rem;
  margin: 0.8rem 0 1.2rem;
  font-size: 0.92rem;
}

section.statements { margin: 1.2rem 0 1.5rem; }
.envtheorem {
  border-left: 3px solid var(--border);
  padding: 0.6rem 0.9rem;
  margin: 0.8rem 0;
  background: #fafafa;
}
.envtheorem-conjecture { border-color: var(--accent); }
.envtheorem-question   { border-color: var(--warn); }
.envtheorem-problem    { border-color: #888; }
.envtheorem-theorem    { border-color: var(--ok); }
.envtheorem strong { display: inline; margin-right: 0.4rem; }

section.keywords {
  font-size: 0.9rem;
  color: var(--muted);
  margin: 1rem 0;
}
.keyword {
  display: inline-block;
  background: var(--code-bg);
  padding: 0.05rem 0.45rem;
  border-radius: 3px;
  color: var(--fg);
}

section.discussion h2,
section.bibliography h2 {
  font-size: 1.05rem;
  margin: 1.5rem 0 0.6rem;
  color: var(--fg);
}
section.bibliography ul {
  list-style: none;
  padding: 0;
  font-size: 0.9rem;
}
section.bibliography li {
  margin: 0.3rem 0;
  padding-left: 1rem;
  text-indent: -1rem;
}
.bib-key { font-size: 0.85rem; color: var(--muted); }
.bib-links { font-size: 0.85rem; color: var(--muted); }
.original { color: var(--ok); }

footer.canonical {
  margin-top: 2rem;
  padding-top: 0.8rem;
  border-top: 1px solid var(--border);
  font-size: 0.88rem;
  color: var(--muted);
}

/* ---------- badges ---------- */

.badge {
  display: inline-block;
  font-size: 0.72rem;
  padding: 0.05rem 0.4rem;
  border-radius: 3px;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  vertical-align: 0.1em;
  font-weight: 600;
}
.badge.erdos { background: #f1e9fb; color: var(--erdos); }
.badge.erdos:hover { text-decoration: none; background: #e7d8f7; }
.badge.undergrad { background: #e6f4ea; color: var(--ok); }

/* ---------- prose pages ---------- */

article.prose { max-width: 760px; }
article.prose h1 { font-size: 1.8rem; margin-bottom: 1rem; }
article.prose h2 { font-size: 1.15rem; margin-top: 1.8rem; }
article.prose code { background: var(--code-bg); padding: 0.05rem 0.3rem; border-radius: 3px; font-size: 0.9em; }

@media (max-width: 780px) {
  .timeline-header {
    display: block;
  }
  .timeline-actions {
    align-items: flex-start;
    margin-top: 0.8rem;
  }
  .timeline-filter-group {
    justify-content: flex-start;
  }
  .timeline-axis {
    display: none;
  }
  .timeline-row {
    grid-template-columns: 1fr;
    gap: 0.3rem;
    padding: 0.65rem 0;
  }
  .timeline-name > span:first-child,
  .timeline-subtitle {
    white-space: normal;
  }
  .timeline-track {
    min-width: 100%;
  }
  .timeline-years {
    justify-content: flex-start;
    flex-wrap: wrap;
  }
}