:root,
:root[data-theme="dark"] {
  --bg: #0f172a;
  --panel: #1e293b;
  --border: #334155;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --code-bg: #0b1120;
  /* syntax highlighting (One Dark palette) */
  --tok-comment: #7f848e;
  --tok-keyword: #c678dd;
  --tok-string: #98c379;
  --tok-number: #d19a66;
  --tok-func: #61afef;
  --tok-builtin: #56b6c2;
  --tok-constant: #d19a66;
  --tok-decorator: #e5c07b;
}

:root[data-theme="light"] {
  --bg: #f8fafc;
  --panel: #ffffff;
  --border: #d8dee9;
  --text: #1e293b;
  --muted: #64748b;
  --accent: #0284c7;
  --code-bg: #f1f5f9;
  /* syntax highlighting (One Light palette) */
  --tok-comment: #a0a1a7;
  --tok-keyword: #a626a4;
  --tok-string: #50a14f;
  --tok-number: #b76b01;
  --tok-func: #4078f2;
  --tok-builtin: #0184bc;
  --tok-constant: #b76b01;
  --tok-decorator: #c18401;
}

body { transition: background 0.2s, color 0.2s; }

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

header {
  padding: 28px 32px 20px;
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  background: var(--bg);
  z-index: 10;
}

.title-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}
header h1 { margin: 0 0 4px; font-size: 1.7rem; }
.subtitle { margin: 0 0 16px; color: var(--muted); }

.theme-btn {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 18px;
  line-height: 1;
  padding: 8px 12px;
  cursor: pointer;
  flex-shrink: 0;
}
.theme-btn:hover { border-color: var(--accent); }

.toolbar {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: center;
}

#search {
  flex: 1 1 280px;
  background: var(--code-bg);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px 14px;
  font-size: 15px;
}

.tag-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 12px;
}
.tag-bar.folded { display: none; }

.tag-filter {
  background: var(--panel);
  color: var(--muted);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 5px 12px;
  font-size: 13px;
  cursor: pointer;
}
.tag-filter:hover { color: var(--text); }
.tag-filter.active {
  background: var(--accent);
  color: #04141f;
  border-color: var(--accent);
  font-weight: 600;
}

.ghost-btn {
  background: transparent;
  color: var(--accent);
  border: 1px solid var(--accent);
  border-radius: 8px;
  padding: 9px 14px;
  font-size: 13px;
  cursor: pointer;
}
.ghost-btn:hover { background: rgba(56, 189, 248, 0.12); }

.count { margin: 14px 0 0; color: var(--muted); font-size: 13px; }

.layout {
  max-width: 1140px;
  margin: 0 auto;
  padding: 24px 32px;
  display: flex;
  gap: 28px;
  align-items: flex-start;
}

.outline {
  flex: 0 0 230px;
  position: sticky;
  top: calc(var(--header-h, 168px) + 16px);
  max-height: calc(100vh - var(--header-h, 168px) - 40px);
  overflow-y: auto;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 16px 18px;
}

.outline h2 {
  margin: 0 0 10px;
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--accent);
}

.outline ol {
  margin: 0;
  padding-left: 22px;
  display: flex;
  flex-direction: column;
  gap: 7px;
}

.outline a {
  color: var(--muted);
  text-decoration: none;
  font-size: 14px;
}
.outline a:hover { color: var(--accent); text-decoration: underline; }

main {
  flex: 1 1 auto;
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: 18px;
}

.card-num { color: var(--accent); }

.card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px 22px;
  scroll-margin-top: calc(var(--header-h, 170px) + 14px);
  min-width: 0;                 /* allow the card to shrink inside flex */
  overflow-wrap: anywhere;      /* break long inline tokens AND shrink min-content */
}

.card-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 12px;
}
.card h2 { margin: 0; font-size: 1.2rem; }

.meta { display: flex; gap: 8px; align-items: center; flex-shrink: 0; }
.date { color: var(--muted); font-size: 12px; }

.diff {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  padding: 2px 8px;
  border-radius: 999px;
}
.diff-easy { background: #14532d; color: #86efac; }
.diff-medium { background: #713f12; color: #fde68a; }
.diff-hard { background: #7f1d1d; color: #fca5a5; }

.tags { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0; }
.chip {
  background: var(--code-bg);
  color: var(--muted);
  border-radius: 6px;
  padding: 2px 9px;
  font-size: 12px;
}

.question { margin: 6px 0 14px; }

.reveal-btn {
  background: var(--accent);
  color: #04141f;
  border: none;
  border-radius: 8px;
  padding: 8px 16px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
}
.reveal-btn:hover { filter: brightness(1.1); }

.answer {
  margin-top: 16px;
  border-top: 1px dashed var(--border);
  padding-top: 14px;
}
.explain { margin-bottom: 12px; }

code {
  background: var(--code-bg);
  padding: 1px 6px;
  border-radius: 4px;
  font-family: "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.9em;
}

pre {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 14px;
  margin: 0;
  max-width: 100%;                    /* never widen the card */
  overflow-x: auto;                   /* long lines scroll instead */
  -webkit-overflow-scrolling: touch;  /* smooth momentum scroll on iOS */
}
pre code {
  background: none;
  padding: 0;
  font-size: 13.5px;
  line-height: 1.6;
}

/* syntax highlight tokens */
.tok-comment { color: var(--tok-comment); font-style: italic; }
.tok-keyword { color: var(--tok-keyword); }
.tok-string { color: var(--tok-string); }
.tok-number { color: var(--tok-number); }
.tok-func { color: var(--tok-func); }
.tok-builtin { color: var(--tok-builtin); }
.tok-constant { color: var(--tok-constant); }
.tok-decorator { color: var(--tok-decorator); }

.empty { color: var(--muted); text-align: center; padding: 40px 0; }

@media (max-width: 760px) {
  .layout { flex-direction: column; padding: 16px; gap: 16px; }
  header { padding: 20px 16px 14px; }
  .outline {
    position: static;
    flex-basis: auto;
    width: 100%;
    min-width: 0;
    max-height: none;
  }
  main { width: 100%; min-width: 0; }
  .card { padding: 16px; }
  pre { padding: 12px; }
  pre code { font-size: 12.5px; }
}

footer {
  text-align: center;
  color: var(--muted);
  font-size: 13px;
  padding: 24px;
  border-top: 1px solid var(--border);
}
footer a { color: var(--accent); text-decoration: none; }
footer a:hover { text-decoration: underline; }