:root {
  --bg: #0f1115;
  --panel: #171a21;
  --panel-border: #2a2e38;
  --text: #e6e8ec;
  --text-dim: #9aa1ad;
  --accent: #5fb3ff;
  --accent-dim: #2c4a63;
  --ok: #4caf7d;
  --ok-bg: #16261f;
  --pending: #d9a441;
  --pending-bg: #2a2216;
  --mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
  line-height: 1.55;
}

.layout {
  display: flex;
  min-height: 100vh;
}

nav.sidebar {
  width: 220px;
  flex-shrink: 0;
  background: var(--panel);
  border-right: 1px solid var(--panel-border);
  padding: 24px 0;
}

nav.sidebar .brand {
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-dim);
  padding: 0 20px 16px;
  border-bottom: 1px solid var(--panel-border);
  margin-bottom: 12px;
}

nav.sidebar a {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  padding: 10px 20px;
  color: var(--text);
  text-decoration: none;
  font-size: 14px;
}

nav.sidebar a:hover { background: var(--panel-border); }
nav.sidebar a.active { background: var(--accent-dim); border-left: 3px solid var(--accent); }

nav.sidebar details {
  border-top: 1px solid var(--panel-border);
  margin-top: 8px;
  padding-top: 4px;
}

nav.sidebar details summary {
  cursor: pointer;
  padding: 10px 20px;
  color: var(--text);
  font-size: 14px;
  list-style: none;
  display: flex;
  align-items: center;
  gap: 8px;
}

nav.sidebar details summary::-webkit-details-marker { display: none; }

nav.sidebar details summary::after {
  content: "\25B8";
  margin-left: auto;
  color: var(--text-dim);
  transition: transform 0.15s ease;
}

nav.sidebar details[open] summary::after { transform: rotate(90deg); }
nav.sidebar details summary:hover { background: var(--panel-border); }

nav.sidebar details a {
  padding-left: 36px;
  font-size: 13px;
}

main {
  flex: 1;
  padding: 40px 56px;
  max-width: 980px;
}

h1 {
  font-size: 26px;
  margin: 0 0 6px;
}

h1 .case-letter {
  color: var(--accent);
  font-family: var(--mono);
}

.subtitle {
  color: var(--text-dim);
  margin: 0 0 28px;
  font-size: 15px;
}

.badge {
  display: inline-block;
  font-size: 12px;
  font-weight: 600;
  padding: 3px 10px;
  border-radius: 999px;
  letter-spacing: 0.02em;
}

.badge.solved { color: var(--ok); background: var(--ok-bg); }
.badge.pending { color: var(--pending); background: var(--pending-bg); }

section.card {
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: 10px;
  padding: 22px 26px;
  margin-bottom: 22px;
}

section.card h2 {
  font-size: 17px;
  margin: 0 0 12px;
  color: var(--accent);
}

section.card h3 {
  font-size: 14px;
  margin: 18px 0 8px;
  color: var(--text);
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-dim);
}

section.card p { margin: 0 0 10px; }
section.card ul { margin: 0 0 10px; padding-left: 20px; }
section.card li { margin-bottom: 6px; }

pre.diagram {
  font-family: var(--mono);
  font-size: 12px;
  line-height: 1.35;
  background: #0b0d11;
  border: 1px solid var(--panel-border);
  border-radius: 8px;
  padding: 18px 20px;
  overflow-x: auto;
  color: #c9e6ff;
}

.diagram-frame {
  background: #ffffff;
  border: 1px solid var(--panel-border);
  border-radius: 10px;
  padding: 20px;
  margin: 14px 0 20px;
  overflow-x: auto;
  text-align: center;
}

.diagram-frame img {
  max-width: 100%;
  height: auto;
}

.diagram-caption {
  font-size: 12px;
  color: var(--text-dim);
  text-align: center;
  margin: -12px 0 20px;
}

.callout {
  border-left: 3px solid var(--accent);
  background: var(--accent-dim);
  padding: 12px 16px;
  border-radius: 0 6px 6px 0;
  margin: 14px 0;
  font-size: 14px;
}

.open-item {
  border-left: 3px solid var(--pending);
  background: var(--pending-bg);
  padding: 10px 14px;
  border-radius: 0 6px 6px 0;
  margin: 8px 0;
  font-size: 13px;
}

table.case-list {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
}

table.case-list th, table.case-list td {
  text-align: left;
  padding: 10px 12px;
  border-bottom: 1px solid var(--panel-border);
}

table.case-list th { color: var(--text-dim); font-weight: 500; font-size: 12px; text-transform: uppercase; }

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

code { font-family: var(--mono); background: #0b0d11; padding: 1px 6px; border-radius: 4px; font-size: 0.9em; }

footer.note {
  margin-top: 30px;
  font-size: 12px;
  color: var(--text-dim);
}

details.expand {
  background: #11151c;
  border: 1px solid var(--panel-border);
  border-radius: 8px;
  margin: 14px 0;
  padding: 4px 0;
}

details.expand summary {
  cursor: pointer;
  padding: 12px 18px;
  color: var(--accent);
  font-size: 14px;
  font-weight: 600;
  list-style: none;
  display: flex;
  align-items: center;
  gap: 8px;
}

details.expand summary::-webkit-details-marker { display: none; }

details.expand summary::before {
  content: "▸";
  display: inline-block;
  transition: transform 0.15s ease;
  color: var(--text-dim);
}

details.expand[open] summary::before {
  transform: rotate(90deg);
}

details.expand summary:hover { color: #8ecbff; }

.expand-body {
  padding: 4px 20px 16px 40px;
  font-size: 14px;
}

.expand-body ol { padding-left: 20px; margin: 10px 0; }
.expand-body li { margin-bottom: 10px; }

.cite {
  font-size: 12px;
  color: var(--text-dim);
  background: #0b0d11;
  border-left: 2px solid var(--accent-dim);
  padding: 8px 12px;
  margin: 10px 0;
  border-radius: 0 4px 4px 0;
}

.cite strong { color: var(--text); }