:root {
  --bg: #0f1419;
  --bg-2: #161c24;
  --bg-3: #1d2530;
  --panel: #19212b;
  --border: #2a3441;
  --text: #e6edf3;
  --text-dim: #9aa7b4;
  --text-faint: #6b7785;
  --accent: #4f9cf9;
  --accent-2: #38bdf8;
  --green: #3fb950;
  --amber: #d29922;
  --purple: #a371f7;
  --red: #f85149;
  --radius: 10px;
  --shadow: 0 4px 24px rgba(0,0,0,.35);
  --maxw: 820px;
}

/* Light (daytime) theme */
:root[data-theme="light"] {
  --bg: #f4f6f9;
  --bg-2: #ffffff;
  --bg-3: #eef1f6;
  --panel: #ffffff;
  --border: #dde3ea;
  --text: #1a2230;
  --text-dim: #51606f;
  --text-faint: #8593a2;
  --accent: #2563eb;
  --accent-2: #0284c7;
  --green: #15803d;
  --amber: #b45309;
  --purple: #7c3aed;
  --red: #dc2626;
  --shadow: 0 4px 20px rgba(31,45,61,.10);
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
body {
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  font-size: 15px;
  line-height: 1.6;
}
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ---------- top bar ---------- */
.topbar {
  display: flex; align-items: center; gap: 24px;
  height: 56px; padding: 0 20px;
  background: var(--bg-2);
  border-bottom: 1px solid var(--border);
  position: sticky; top: 0; z-index: 20;
}
.brand { display: flex; align-items: center; gap: 10px; font-weight: 700; }
.brand-mark {
  display: inline-grid; place-items: center;
  width: 30px; height: 30px; border-radius: 8px;
  background: linear-gradient(135deg, var(--accent), var(--purple));
  color: white; font-size: 18px; font-weight: 800;
}
.brand-title { font-size: 16px; letter-spacing: .2px; }
.topnav { display: flex; gap: 6px; }
.topnav a {
  padding: 7px 14px; border-radius: 8px; color: var(--text-dim); font-weight: 600;
}
.topnav a:hover { background: var(--bg-3); text-decoration: none; color: var(--text); }
.topnav a.active { background: var(--bg-3); color: var(--text); }
.toolbar { margin-left: auto; display: flex; gap: 8px; }
.tool-btn {
  background: var(--bg-3); color: var(--text-dim); border: 1px solid var(--border);
  padding: 6px 12px; border-radius: 8px; font-size: 13px; cursor: pointer; font-weight: 600;
}
.tool-btn:hover { color: var(--text); border-color: var(--accent); }
.tool-btn.danger:hover { color: var(--red); border-color: var(--red); }
.theme-btn { font-size: 15px; padding: 5px 10px; line-height: 1; }

/* ---------- layout ---------- */
.layout { display: flex; min-height: calc(100vh - 56px); }
.sidebar {
  width: 290px; flex-shrink: 0;
  background: var(--bg-2);
  border-right: 1px solid var(--border);
  padding: 16px 10px 40px;
  overflow-y: auto;
  height: calc(100vh - 56px);
  position: sticky; top: 56px;
}
.main { flex: 1; min-width: 0; }
.view-pad { max-width: var(--maxw); margin: 0 auto; padding: 30px 28px 80px; }

/* ---------- sidebar content ---------- */
.side-chapter { margin-bottom: 18px; }
.side-chapter-head { display: flex; align-items: baseline; gap: 8px; padding: 0 8px; }
.side-ch-num { font-size: 11px; color: var(--text-faint); font-weight: 700; text-transform: uppercase; }
.side-ch-title { font-weight: 700; font-size: 14px; }
.side-ch-prog { display: flex; align-items: center; gap: 8px; padding: 4px 8px 6px; }
.side-ch-pct { font-size: 11px; color: var(--text-faint); white-space: nowrap; }
.side-topics { display: flex; flex-direction: column; }
.side-topic {
  display: flex; align-items: center; gap: 8px;
  padding: 6px 8px; border-radius: 7px; color: var(--text-dim); font-size: 13px;
}
.side-topic:hover { background: var(--bg-3); text-decoration: none; color: var(--text); }
.side-topic.active { background: var(--bg-3); color: var(--text); box-shadow: inset 2px 0 0 var(--accent); }
.side-topic-id { font-size: 11px; color: var(--text-faint); width: 26px; flex-shrink: 0; }
.side-topic-title { flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.side-topic-count {
  font-size: 11px; background: var(--bg); border: 1px solid var(--border);
  border-radius: 10px; padding: 0 7px; color: var(--text-dim);
}
.side-topic-soon { font-size: 10px; color: var(--text-faint); font-style: italic; }

/* ---------- progress bar ---------- */
.bar { flex: 1; height: 6px; background: var(--bg); border-radius: 6px; overflow: hidden; }
.bar-fill { height: 100%; background: linear-gradient(90deg, var(--accent), var(--green)); border-radius: 6px; transition: width .3s; }

/* ---------- headings ---------- */
h1 { font-size: 26px; margin: 0 0 6px; letter-spacing: -.3px; }
h2 { font-size: 18px; margin: 34px 0 14px; }
h3 { font-size: 14px; text-transform: uppercase; letter-spacing: .6px; color: var(--text-dim); margin: 0 0 8px; }
.subtle { color: var(--text-dim); }
.breadcrumb { font-size: 13px; color: var(--text-faint); margin-bottom: 10px; }

/* ---------- dashboard ---------- */
.stat-cards { display: grid; grid-template-columns: repeat(5, 1fr); gap: 12px; margin: 22px 0; }
.stat-card {
  background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 16px; text-align: center;
}
.stat-card.accent { border-color: var(--amber); }
.stat-num { font-size: 26px; font-weight: 800; }
.stat-lbl { font-size: 12px; color: var(--text-dim); margin-top: 2px; }
.overall {
  background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 18px 20px; margin-bottom: 12px;
}
.overall-top { display: flex; justify-content: space-between; font-size: 13px; color: var(--text-dim); margin-bottom: 10px; }
.overall .bar { height: 10px; }
.overall-pct { text-align: right; font-size: 12px; color: var(--text-faint); margin-top: 6px; }

.dash-chapters { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.dash-chapter {
  display: block; background: var(--panel); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 16px 18px; color: var(--text);
}
.dash-chapter:hover { border-color: var(--accent); text-decoration: none; }
.dash-ch-head { display: flex; justify-content: space-between; gap: 10px; font-size: 14px; }
.dash-ch-head span { color: var(--text-faint); font-size: 12px; white-space: nowrap; }
.dash-ch-blurb { font-size: 12.5px; color: var(--text-dim); margin: 6px 0 12px; line-height: 1.5; }
.dash-ch-meta { font-size: 11.5px; color: var(--text-faint); margin-top: 8px; }

/* ---------- problem list rows ---------- */
.prob-list { display: flex; flex-direction: column; gap: 8px; }
.prob-row {
  display: flex; align-items: center; gap: 12px;
  background: var(--panel); border: 1px solid var(--border);
  border-radius: 9px; padding: 11px 14px; color: var(--text);
}
.prob-row:hover { border-color: var(--accent); text-decoration: none; background: var(--bg-3); }
.prob-row.soon { opacity: .55; cursor: default; }
.prob-row-title { flex: 1; font-weight: 600; }
.prob-row-meta { font-size: 12px; color: var(--text-faint); white-space: nowrap; }

.status-dot {
  width: 22px; height: 22px; flex-shrink: 0; border-radius: 50%;
  display: grid; place-items: center; font-size: 12px; font-weight: 700;
  border: 1.5px solid var(--border); background: var(--bg);
}
.status-dot.st-unseen { color: var(--text-faint); }
.status-dot.st-attempting { color: var(--amber); border-color: var(--amber); }
.status-dot.st-solved { color: var(--green); border-color: var(--green); background: rgba(63,185,80,.12); }
.status-dot.st-review { color: var(--purple); border-color: var(--purple); }

/* ---------- badges & tags ---------- */
.badge { font-size: 11px; font-weight: 700; padding: 2px 9px; border-radius: 20px; border: 1px solid; white-space: nowrap; }
.d-easy { color: var(--green); border-color: var(--green); }
.d-medium { color: var(--amber); border-color: var(--amber); }
.d-hard { color: var(--red); border-color: var(--red); }
.soon-badge { color: var(--text-faint); border-color: var(--border); }
.tag {
  font-size: 11px; color: var(--text-dim); background: var(--bg-3);
  border: 1px solid var(--border); border-radius: 6px; padding: 2px 8px; margin-right: 4px;
}

/* ---------- topic note ---------- */
.topic-note {
  background: var(--bg-3); border-left: 3px solid var(--accent);
  border-radius: 6px; padding: 4px 16px; margin: 14px 0 20px; color: var(--text-dim); font-size: 14px;
}

/* ---------- filters ---------- */
.filters {
  display: flex; flex-wrap: wrap; align-items: center; gap: 14px 18px;
  background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 14px 16px; margin: 18px 0;
}
.f-search {
  flex: 1; min-width: 200px; background: var(--bg); border: 1px solid var(--border);
  color: var(--text); padding: 9px 12px; border-radius: 8px; font-size: 14px;
}
.f-search:focus { outline: none; border-color: var(--accent); }
.f-group { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.f-label { font-size: 12px; color: var(--text-faint); font-weight: 600; }
.f-group label, .f-toggle { font-size: 13px; color: var(--text-dim); display: inline-flex; align-items: center; gap: 5px; cursor: pointer; }
.filters input[type="checkbox"] { accent-color: var(--accent); }
.browse-count { font-size: 13px; color: var(--text-faint); margin-bottom: 12px; }

/* ---------- problem detail ---------- */
.problem-head { display: flex; align-items: center; gap: 14px; }
.problem-head h1 { flex: 1; }
.star-btn { background: none; border: none; color: var(--text-faint); font-size: 26px; cursor: pointer; line-height: 1; }
.star-btn.on { color: var(--amber); }
.problem-meta { display: flex; align-items: center; gap: 6px; flex-wrap: wrap; margin: 6px 0 18px; }

.status-row { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; margin-bottom: 22px; }
.status-row-lbl { font-size: 13px; color: var(--text-faint); margin-right: 4px; }
.status-btn {
  background: var(--bg-3); border: 1px solid var(--border); color: var(--text-dim);
  padding: 6px 14px; border-radius: 8px; cursor: pointer; font-size: 13px; font-weight: 600;
}
.status-btn:hover { color: var(--text); }
.status-btn.on.st-attempting { background: rgba(210,153,34,.15); color: var(--amber); border-color: var(--amber); }
.status-btn.on.st-solved { background: rgba(63,185,80,.15); color: var(--green); border-color: var(--green); }
.status-btn.on.st-review { background: rgba(163,113,247,.15); color: var(--purple); border-color: var(--purple); }
.status-btn.on.st-unseen { background: var(--bg); color: var(--text); }

.block {
  background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 18px 22px; margin-bottom: 14px;
}
.block.statement { border-left: 3px solid var(--accent); }
.block p { margin: 0 0 10px; }
.block p:last-child { margin-bottom: 0; }
.statement { font-size: 15.5px; }

.reveal summary {
  cursor: pointer; font-weight: 700; color: var(--accent-2); list-style: none;
  padding: 2px 0; user-select: none;
}
.reveal summary::-webkit-details-marker { display: none; }
.reveal summary:hover { color: var(--accent); }
.reveal[open] summary { margin-bottom: 12px; border-bottom: 1px solid var(--border); padding-bottom: 10px; }
.reveal.solution summary { color: var(--green); }
.reveal-body { color: var(--text); }
.reveal-body ol, .reveal-body ul { padding-left: 22px; }
.reveal-body li { margin-bottom: 4px; }

.key-idea { border-left: 3px solid var(--purple); }
.key-idea p { color: var(--text-dim); }

.notes textarea {
  width: 100%; min-height: 100px; resize: vertical;
  background: var(--bg); border: 1px solid var(--border); color: var(--text);
  border-radius: 8px; padding: 12px; font-size: 14px; font-family: inherit; line-height: 1.5;
}
.notes textarea:focus { outline: none; border-color: var(--accent); }
.notes-saved { font-size: 12px; color: var(--green); height: 16px; margin-top: 4px; }

.soon-panel {
  background: var(--bg-3); border: 1px dashed var(--border); border-radius: var(--radius);
  padding: 24px; color: var(--text-dim); text-align: center; line-height: 1.7; margin: 16px 0;
}

.nav-buttons { display: flex; justify-content: space-between; gap: 12px; margin-top: 26px; }
.nav-btn {
  background: var(--panel); border: 1px solid var(--border); border-radius: 8px;
  padding: 10px 16px; color: var(--text-dim); font-size: 13px; font-weight: 600; max-width: 46%;
  overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
}
.nav-btn:hover { border-color: var(--accent); color: var(--text); text-decoration: none; }
.nav-btn.next { text-align: right; margin-left: auto; }

/* tables inside solutions */
.reveal-body table, .block table {
  border-collapse: collapse; margin: 12px 0; font-size: 13.5px; width: auto;
}
.reveal-body th, .reveal-body td, .block th, .block td {
  border: 1px solid var(--border); padding: 6px 12px; text-align: center;
}
.reveal-body th, .block th { background: var(--bg-3); font-weight: 700; color: var(--text-dim); }

/* code blocks & inline code */
.reveal-body pre, .block pre {
  background: var(--bg); border: 1px solid var(--border); border-radius: 8px;
  padding: 12px 14px; overflow-x: auto; margin: 12px 0;
}
.reveal-body pre code, .block pre code { background: none; border: none; padding: 0; }
.reveal-body code, .block code {
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
  font-size: 13px; background: var(--bg-3); border: 1px solid var(--border);
  border-radius: 5px; padding: 1px 5px; color: var(--accent-2);
}

/* katex sizing */
.katex { font-size: 1.05em; }
.katex-display { margin: 14px 0; overflow-x: auto; overflow-y: hidden; }

/* ---------- language + auth in toolbar ---------- */
.lang-btn { font-weight: 700; letter-spacing: .3px; }
.auth-slot { display: inline-flex; align-items: center; gap: 8px; }
.auth-user { display: inline-flex; align-items: center; gap: 7px; }
.auth-avatar {
  width: 24px; height: 24px; border-radius: 50%; object-fit: cover;
  border: 1px solid var(--border);
}
.auth-avatar-fallback {
  display: inline-grid; place-items: center; font-size: 12px; font-weight: 700;
  background: linear-gradient(135deg, var(--accent), var(--purple)); color: #fff;
}
.auth-name {
  font-size: 13px; color: var(--text-dim); font-weight: 600; max-width: 120px;
  overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
}
.tool-btn.auth-signin { border-color: var(--accent); color: var(--accent); }
.tool-btn.auth-signin:hover { background: var(--accent); color: #fff; }

/* ---------- My List count chip ---------- */
.count-chip {
  font-size: 12px; font-weight: 700; color: var(--text-dim);
  background: var(--bg-3); border: 1px solid var(--border);
  border-radius: 20px; padding: 1px 9px; margin-left: 6px; vertical-align: middle;
}

/* ---------- discussion forum ---------- */
.forum { border-left: 3px solid var(--accent-2); }
.forum-guidelines {
  font-size: 12.5px; color: var(--text-dim); background: var(--bg-3);
  border: 1px solid var(--border); border-radius: 8px; padding: 9px 13px; margin-bottom: 14px;
  line-height: 1.5;
}
.forum-signin {
  display: flex; align-items: center; gap: 14px; flex-wrap: wrap;
  background: var(--bg-3); border: 1px dashed var(--border); border-radius: 8px;
  padding: 14px 16px; color: var(--text-dim); font-size: 14px; margin-bottom: 8px;
}
.forum-text {
  width: 100%; min-height: 80px; resize: vertical;
  background: var(--bg); border: 1px solid var(--border); color: var(--text);
  border-radius: 8px; padding: 11px 12px; font-size: 14px; font-family: inherit; line-height: 1.5;
}
.forum-text:focus { outline: none; border-color: var(--accent); }
.forum-composer-row { display: flex; justify-content: flex-end; margin-top: 8px; }
.post-btn {
  background: var(--accent); color: #fff; border: none; border-radius: 8px;
  padding: 8px 20px; font-size: 13px; font-weight: 700; cursor: pointer;
}
.post-btn:hover { filter: brightness(1.08); }
.post-btn:disabled { opacity: .6; cursor: default; }
.forum-list { margin-top: 18px; display: flex; flex-direction: column; gap: 14px; }
.cm { border-top: 1px solid var(--border); padding-top: 14px; }
.cm:first-child { border-top: none; padding-top: 0; }
.cm-head { display: flex; align-items: center; gap: 8px; margin-bottom: 6px; }
.cm-avatar {
  width: 26px; height: 26px; border-radius: 50%; object-fit: cover; border: 1px solid var(--border);
}
.cm-avatar-fallback {
  display: inline-grid; place-items: center; font-size: 12px; font-weight: 700;
  background: linear-gradient(135deg, var(--accent), var(--purple)); color: #fff;
}
.cm-name { font-weight: 700; font-size: 13.5px; }
.cm-time { font-size: 11.5px; color: var(--text-faint); }
.cm-body { font-size: 14px; line-height: 1.55; white-space: pre-wrap; word-break: break-word; }
.cm-actions { margin-top: 6px; }
.cm-link {
  background: none; border: none; color: var(--text-faint); font-size: 12px;
  cursor: pointer; padding: 0; font-weight: 600;
}
.cm-link:hover { color: var(--accent); }
.cm-del:hover { color: var(--red); }

/* ---------- leaderboard ---------- */
.lb-table { width: 100%; border-collapse: collapse; margin-top: 18px; }
.lb-table thead th {
  text-align: left; font-size: 11px; text-transform: uppercase; letter-spacing: .6px;
  color: var(--text-faint); font-weight: 700; padding: 8px 12px; border-bottom: 1px solid var(--border);
}
.lb-table td { padding: 10px 12px; border-bottom: 1px solid var(--border); }
.lb-table .lb-rank { width: 64px; text-align: center; font-weight: 700; font-size: 15px; }
.lb-table th.lb-solved, .lb-table td.lb-solved { text-align: right; width: 90px; font-weight: 700; }
.lb-userc { display: flex; align-items: center; gap: 9px; }
.lb-avatar { width: 28px; height: 28px; border-radius: 50%; object-fit: cover; border: 1px solid var(--border); }
.lb-avatar-fallback {
  display: inline-grid; place-items: center; font-size: 12px; font-weight: 700;
  background: linear-gradient(135deg, var(--accent), var(--purple)); color: #fff;
}
.lb-name { font-weight: 600; }
.lb-youtag {
  font-size: 11px; font-weight: 700; color: var(--accent); background: rgba(79,156,249,.14);
  border-radius: 20px; padding: 1px 8px; margin-left: 2px;
}
.lb-me { background: rgba(79,156,249,.08); }
.lb-me td:first-child { box-shadow: inset 3px 0 0 var(--accent); }

/* ---------- responsive ---------- */
@media (max-width: 860px) {
  .stat-cards { grid-template-columns: repeat(2, 1fr); }
  .dash-chapters { grid-template-columns: 1fr; }
  .sidebar { display: none; }
  .auth-name { display: none; }
}