:root {
  /* THEME: Premium Warm Neutral + Emerald accent */
  --bg: #ffffff;
  --bg-alt: #f8f7f4;
  --text: #1c1917;
  --muted: #6b6660;
  --border: #e7e3dc;
  --accent: #047857;
  --accent-soft: #d1fae5;
  --sidebar-bg: #faf9f6;
  --sidebar-text: #1c1917;
  --sidebar-muted: #6b6660;
  --sidebar-border: #e7e3dc;
  --sidebar-card: #ffffff;
  --sidebar-hover: #f0ede5;
  --topic-hover: #f0ede5;
  --done: #16a34a;
  --code-bg: #f4f3ef;
}

[data-theme="dark"] {
  --bg: #1a1816;
  --bg-alt: #25221f;
  --text: #ebe5db;
  --muted: #a39c92;
  --border: #3a3631;
  --accent: #34d399;
  --accent-soft: #064e3b;
  --sidebar-bg: #1a1816;
  --sidebar-text: #ebe5db;
  --sidebar-muted: #a39c92;
  --sidebar-border: #3a3631;
  --sidebar-card: #25221f;
  --sidebar-hover: #2f2b27;
  --topic-hover: #2f2b27;
  --done: #4ade80;
  --code-bg: #25221f;
}

* { box-sizing: border-box; }

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

.topbar {
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 0.75rem 1rem;
  background: var(--bg-alt);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}

.topbar h1 {
  font-size: 1.1rem;
  margin: 0;
  flex: 1;
}

.topbar button {
  background: none;
  border: 1px solid var(--border);
  color: var(--text);
  font-size: 1.1rem;
  padding: 0.35rem 0.6rem;
  border-radius: 6px;
  cursor: pointer;
}

.topbar button:hover {
  background: var(--topic-hover);
}

.layout {
  display: flex;
  min-height: calc(100vh - 56px);
}

.sidebar {
  width: 280px;
  background: var(--sidebar-bg);
  color: var(--sidebar-text, var(--text));
  border-right: 1px solid var(--sidebar-border, var(--border));
  padding: 1rem 0.5rem;
  overflow-y: auto;
  height: calc(100vh - 56px);
  position: sticky;
  top: 56px;
}

.sidebar .topic-link { color: var(--sidebar-text, var(--text)); }
.sidebar .topic-link:hover { background: var(--sidebar-hover, var(--topic-hover)); }
.sidebar .topics { border-left-color: var(--sidebar-border, var(--border)); }

.sidebar.hidden { display: none; }

.subject {
  margin-bottom: 0.4rem;
}

.subject-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.5rem 0.75rem;
  cursor: pointer;
  border-radius: 6px;
  font-weight: 600;
  user-select: none;
  transition: background 0.15s, color 0.15s;
}

.subject-header:hover { background: var(--topic-hover); }

.subject-header .arrow {
  transition: transform 0.2s;
  font-size: 0.8rem;
  color: var(--muted);
}

.subject.open > .subject-header > .arrow { transform: rotate(90deg); }

.subject-icon {
  display: inline-block;
  margin-right: 0.35rem;
  font-size: 1rem;
}

.topics {
  display: none;
  padding-left: 0.6rem;
  margin-top: 0.2rem;
  margin-left: 0.4rem;
  border-left: 2px dashed var(--border);
}

.subject.open > .topics { display: block; }

.topic-link {
  display: block;
  padding: 0.4rem 0.75rem;
  margin: 2px 0;
  border-radius: 4px;
  cursor: pointer;
  font-size: 0.92rem;
  color: var(--text);
  text-decoration: none;
  border-left: 3px solid transparent;
  transition: background 0.15s, border-color 0.15s, padding 0.15s;
}

.topic-link:hover {
  background: var(--topic-hover);
  border-left-color: var(--subject-color, var(--accent));
  padding-left: 0.95rem;
}

.topic-link.active {
  background: var(--accent-soft);
  border-left-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}

.topic-link.read::before {
  content: "✓ ";
  color: var(--done);
  font-weight: bold;
}

/* ===== PER-SUBJECT COLOR THEMING ===== */

/* Top-level subject card */
.subject-root {
  background: var(--sidebar-card, var(--bg));
  border: 1px solid var(--sidebar-border, var(--border));
  border-left: 4px solid var(--accent);
  border-radius: 8px;
  margin-bottom: 0.6rem;
  overflow: hidden;
  box-shadow: 0 1px 2px rgba(0,0,0,0.08);
}

.subject-root-header {
  background: transparent;
  color: var(--accent);
  border-radius: 0;
  padding: 0.7rem 0.85rem;
  font-size: 0.98rem;
}

.subject-root-header:hover {
  filter: brightness(0.97);
  background: var(--subject-soft, var(--accent-soft));
}

.subject-root > .topics {
  padding: 0.4rem 0.5rem;
  margin-left: 0;
  border-left: none;
}

/* Section header (Grammar, Vocabulary, Arithmetic, etc.) */
.section-wrap > .section-header {
  font-size: 0.85rem;
  padding: 0.4rem 0.6rem;
  margin-top: 0.15rem;
  color: var(--sidebar-muted, var(--muted));
  background: transparent;
  border-left: 2px solid var(--sidebar-border, var(--border));
  border-radius: 0;
  margin-left: 0.3rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  font-weight: 600;
}

.section-wrap > .section-header:hover {
  background: var(--sidebar-hover, var(--topic-hover));
  color: var(--accent);
  border-left-color: var(--accent);
}

.section-wrap.open > .section-header {
  color: var(--accent);
  border-left-color: var(--accent);
  font-weight: 700;
}

/* Group headers (Ancient History, Medieval History, etc. inside History) */
.group-wrap > .subject-header {
  color: var(--subject-color, var(--accent)) !important;
  font-size: 0.82rem !important;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  background: transparent;
}

/* All subjects use the default accent color */
.subject-root {
  --subject-color: var(--accent);
  --subject-soft: var(--accent-soft);
}

.placeholder {
  color: var(--muted);
  font-style: italic;
  padding: 0.4rem 0.75rem;
  font-size: 0.85rem;
}

.content {
  flex: 1;
  padding: 2rem 3rem;
  max-width: 900px;
  margin: 0 auto;
  width: 100%;
}

.content h2 {
  border-bottom: 2px solid var(--accent);
  padding-bottom: 0.4rem;
  margin-top: 0;
}

.content h3 {
  color: var(--accent);
  margin-top: 1.8rem;
}

.content h4 {
  margin-top: 1.2rem;
  color: var(--muted);
}

.content p, .content ul, .content ol { font-size: 1rem; }

.content table {
  border-collapse: collapse;
  width: 100%;
  margin: 1rem 0;
  font-size: 0.94rem;
}

.content th, .content td {
  border: 1px solid var(--border);
  padding: 0.55rem 0.75rem;
  text-align: left;
  vertical-align: top;
}

.content th {
  background: var(--bg-alt);
  font-weight: 600;
}

.content blockquote {
  border-left: 4px solid var(--accent);
  margin: 1rem 0;
  padding: 0.5rem 1rem;
  background: var(--bg-alt);
  color: var(--muted);
}

.content code {
  background: var(--code-bg);
  padding: 0.1rem 0.4rem;
  border-radius: 3px;
  font-size: 0.9em;
}

.content figure {
  margin: 1.2rem 0;
  text-align: center;
}

.content figure img {
  max-width: 100%;
  max-height: 420px;
  height: auto;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: #fff;
}

.content figcaption {
  margin-top: 0.4rem;
  font-size: 0.88rem;
  color: var(--muted);
  font-style: italic;
}

.content .img-row {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  justify-content: center;
  margin: 1.2rem 0;
}

.content .img-row figure {
  flex: 1 1 280px;
  max-width: 360px;
  margin: 0;
}

/* Solution block styling — step-by-step layout */
.content p:has(b:first-child) b:first-child:not(:only-child) {
  /* nothing — handled per-element below */
}

.content h4 + p {
  margin-top: 0.4rem;
}

.content p > b:first-child {
  color: var(--accent);
}

/* Make <br> in Solution paragraphs feel like list spacing */
.content p {
  line-height: 1.7;
}

.content p > br {
  display: block;
  content: "";
  margin-bottom: 0.2rem;
}

.topic-meta {
  display: flex;
  gap: 1rem;
  align-items: center;
  margin-bottom: 1rem;
  padding: 0.6rem 1rem;
  background: var(--bg-alt);
  border-radius: 8px;
  font-size: 0.9rem;
  color: var(--muted);
}

.btn {
  padding: 0.5rem 1rem;
  border: 1px solid var(--accent);
  background: var(--accent);
  color: white;
  border-radius: 6px;
  cursor: pointer;
  font-size: 0.9rem;
}

.btn.secondary {
  background: transparent;
  color: var(--accent);
}

.btn:hover { opacity: 0.9; }

.quiz {
  margin-top: 2rem;
  padding: 1.5rem;
  background: var(--bg-alt);
  border-radius: 10px;
  border: 1px solid var(--border);
}

.quiz h3 { margin-top: 0; }

.question {
  margin-bottom: 1.5rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--border);
}

.question:last-child { border-bottom: none; }

.question-text {
  font-weight: 500;
  margin-bottom: 0.6rem;
}

.options { list-style: none; padding: 0; margin: 0; }

.option {
  display: block;
  padding: 0.6rem 0.9rem;
  margin: 0.3rem 0;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  cursor: pointer;
  transition: all 0.15s;
}

.option:hover { border-color: var(--accent); }

.option.selected { border-color: var(--accent); background: var(--accent-soft); }

.option.correct {
  background: rgba(22, 163, 74, 0.15);
  border-color: var(--done);
}

.option.wrong {
  background: rgba(220, 38, 38, 0.15);
  border-color: #dc2626;
}

.explanation {
  margin-top: 0.6rem;
  padding: 0.6rem 0.9rem;
  background: var(--accent-soft);
  border-radius: 6px;
  font-size: 0.9rem;
  display: none;
}

.explanation.show { display: block; }

.score-banner {
  margin-top: 1rem;
  padding: 1rem;
  background: var(--accent-soft);
  border-radius: 8px;
  font-weight: 500;
  text-align: center;
}

.topic-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 3rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border);
}

@media (max-width: 768px) {
  .sidebar { position: fixed; z-index: 20; height: calc(100vh - 56px); }
  .content { padding: 1.2rem; }
}