:root {
  --bg: #f7f7f9;
  --panel: #ffffff;
  --border: #d7d7dc;
  --text: #1f2430;
  --muted: #6b7280;
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --error-bg: #fef2f2;
  --error-border: #fecaca;
  --error-text: #991b1b;
  --ok-bg: #f0fdf4;
  --ok-border: #bbf7d0;
  --ok-text: #166534;
}

* { 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: 1.5;
}

header {
  padding: 24px 20px 12px;
  text-align: center;
}
header h1 { margin: 0 0 4px; font-size: 1.8rem; }
.subtitle { color: var(--muted); margin: 0; }

main {
  max-width: 900px;
  margin: 0 auto;
  padding: 0 20px 60px;
  display: flex;
  flex-direction: column;
  gap: 24px;
}

section {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 18px 20px;
}
section h2 { margin-top: 0; font-size: 1.15rem; }
.hint { color: var(--muted); font-size: 0.92rem; margin-top: -6px; }

.puzzle-selector {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.puzzle-btn {
  padding: 8px 14px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: #f3f4f6;
  cursor: pointer;
  font-size: 0.95rem;
}
.puzzle-btn.selected {
  background: var(--accent);
  color: white;
  border-color: var(--accent);
}

.palette {
  display: flex;
  gap: 10px;
  margin-bottom: 14px;
}
.swatch {
  width: 40px;
  height: 40px;
  border-radius: 8px;
  border: 2px solid var(--border);
  cursor: pointer;
}
.swatch.selected {
  border-color: var(--text);
  box-shadow: 0 0 0 2px var(--text);
}

.net-container {
  display: flex;
  justify-content: center;
  padding: 10px 0 4px;
  overflow: visible;
}

.puzzle3d-wrap {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  width: 100%;
}

.drag-hint {
  margin: 0;
  color: var(--muted);
  font-size: 0.82rem;
  text-align: center;
  user-select: none;
}

/* ---------- cube family + pyraminx: real WebGL (Three.js) scenes ---------- */

.three-canvas-host {
  display: flex;
  justify-content: center;
  touch-action: none;
}
.three-canvas-host canvas {
  cursor: grab;
  border-radius: 8px;
}
.three-canvas-host canvas:active {
  cursor: grabbing;
}

.actions {
  margin-top: 16px;
  display: flex;
  gap: 10px;
}
.primary-btn, .secondary-btn {
  padding: 10px 20px;
  border-radius: 8px;
  border: 1px solid var(--border);
  font-size: 1rem;
  cursor: pointer;
}
.primary-btn {
  background: var(--accent);
  color: white;
  border-color: var(--accent);
}
.primary-btn:hover { background: var(--accent-hover); }
.primary-btn:disabled {
  background: #9ca3af;
  border-color: #9ca3af;
  cursor: not-allowed;
}
.secondary-btn { background: #f3f4f6; }

.note {
  margin-top: 10px;
  padding: 10px 14px;
  border-radius: 8px;
  background: #fffbeb;
  border: 1px solid #fde68a;
  color: #92400e;
}

#validation-messages { margin-top: 14px; }
.error-box, .ok-box {
  border-radius: 8px;
  padding: 12px 16px;
  font-size: 0.95rem;
}
.error-box {
  background: var(--error-bg);
  border: 1px solid var(--error-border);
  color: var(--error-text);
}
.error-box ul { margin: 6px 0 0; padding-left: 20px; }
.ok-box {
  background: var(--ok-bg);
  border: 1px solid var(--ok-border);
  color: var(--ok-text);
}

#results-section:empty { display: none; }
.stage {
  border-top: 1px solid var(--border);
  padding: 12px 0;
}
.stage:first-of-type { border-top: none; }
.stage h3 { margin: 0 0 4px; font-size: 1.02rem; }
.stage-desc { color: var(--muted); margin: 0 0 8px; font-size: 0.92rem; }
.stage-moves { margin: 0; }
.move {
  display: inline-block;
  background: #eef2ff;
  border: 1px solid #c7d2fe;
  border-radius: 5px;
  padding: 2px 8px;
  margin: 2px 2px 0 0;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-weight: 600;
}

footer {
  text-align: center;
  color: var(--muted);
  font-size: 0.85rem;
  padding: 20px;
}

/* ---------- site-wide header / nav / footer (js/ui/layout.js) ---------- */

.site-header-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
  padding: 14px 20px;
  background: var(--panel);
  border-bottom: 1px solid var(--border);
}
.site-brand {
  font-weight: 700;
  font-size: 1.15rem;
  color: var(--text);
  text-decoration: none;
}
.site-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
}
.site-nav-link {
  padding: 6px 12px;
  border-radius: 8px;
  color: var(--muted);
  text-decoration: none;
  font-size: 0.95rem;
}
.site-nav-link:hover { background: #f3f4f6; color: var(--text); }
.site-nav-link.selected { background: var(--accent); color: white; }

.site-footer-inner {
  max-width: 900px;
  margin: 0 auto;
  padding: 28px 20px 24px;
  text-align: center;
  color: var(--muted);
  font-size: 0.85rem;
}
.site-footer-nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 14px;
  margin-bottom: 12px;
}
.site-footer-nav a { color: var(--muted); text-decoration: none; }
.site-footer-nav a:hover { color: var(--text); text-decoration: underline; }
.site-footer-desc { max-width: 640px; margin: 0 auto 6px; }
.site-footer-legal { margin: 0; }

/* ---------- ad slots (ads/adsterra.js) ---------- */

.ad-slot {
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 16px 0;
  overflow: hidden;
}
/* Reserved heights match common Adsterra unit sizes so a slot loading its
   real ad doesn't shift surrounding layout (helps Core Web Vitals/CLS). */
.ad-slot-banner { min-height: 90px; }
.ad-slot-native-banner { min-height: 250px; }

/* ---------- home page hero + feature cards ---------- */

.hero {
  text-align: center;
  padding: 36px 20px 8px;
}
.hero h1 { margin: 0 0 8px; font-size: 2rem; }
.hero p { color: var(--muted); max-width: 640px; margin: 0 auto; }

.feature-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 16px;
}
.feature-card {
  display: block;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 18px 20px;
  text-decoration: none;
  color: inherit;
}
.feature-card:hover { border-color: var(--accent); }
.feature-card h3 { margin: 0 0 6px; font-size: 1.05rem; color: var(--text); }
.feature-card p { margin: 0; color: var(--muted); font-size: 0.92rem; }
.feature-card .badge {
  display: inline-block;
  font-size: 0.75rem;
  color: var(--muted);
  background: #f3f4f6;
  border-radius: 6px;
  padding: 2px 8px;
  margin-bottom: 8px;
}

/* ---------- long-form content (tutorials, history, blog posts) ---------- */

.prose { max-width: 720px; margin: 0 auto; }
.prose h2 { margin-top: 28px; font-size: 1.25rem; }
.prose h2:first-child { margin-top: 0; }
.prose h3 { margin-top: 20px; font-size: 1.05rem; }
.prose p { margin: 12px 0; }
.prose ul, .prose ol { padding-left: 22px; margin: 12px 0; }
.prose li { margin: 4px 0; }
.prose .move {
  display: inline-block;
  background: #eef2ff;
  border: 1px solid #c7d2fe;
  border-radius: 5px;
  padding: 2px 8px;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-weight: 600;
}
.page-meta { color: var(--muted); font-size: 0.85rem; margin: -8px 0 8px; }

/* ---------- FAQ (details/summary, also used for FAQPage schema) ---------- */

.faq { max-width: 720px; margin: 28px auto 0; }
.faq h2 { margin: 0 0 12px; font-size: 1.25rem; }
.faq details {
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 16px;
  margin-bottom: 10px;
}
.faq summary {
  cursor: pointer;
  font-weight: 600;
  list-style: none;
}
.faq summary::-webkit-details-marker { display: none; }
.faq summary::before { content: '+ '; color: var(--accent); }
.faq details[open] summary::before { content: '\2212 '; }
.faq details p { margin: 10px 0 2px; color: var(--text); }

/* ---------- algorithm library ---------- */

.algo-filters {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 16px;
}
.algo-filter-btn {
  padding: 6px 12px;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: #f3f4f6;
  cursor: pointer;
  font-size: 0.88rem;
}
.algo-filter-btn.selected {
  background: var(--accent);
  color: white;
  border-color: var(--accent);
}
.algo-list {
  display: flex;
  flex-direction: column;
  gap: 12px;
}
.algo-card {
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 14px 16px;
}
.algo-card h3 { margin: 0 0 4px; font-size: 1rem; }
.algo-card .algo-meta { color: var(--muted); font-size: 0.8rem; margin-bottom: 8px; }
.algo-card .algo-notation {
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  background: #eef2ff;
  border: 1px solid #c7d2fe;
  border-radius: 6px;
  padding: 6px 10px;
  display: inline-block;
  margin-bottom: 8px;
  font-weight: 600;
}
.algo-card p { margin: 0; color: var(--text); font-size: 0.92rem; }

/* ---------- blog ---------- */

.blog-list {
  display: flex;
  flex-direction: column;
  gap: 14px;
}
.blog-card {
  display: block;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 16px 18px;
  text-decoration: none;
  color: inherit;
}
.blog-card:hover { border-color: var(--accent); }
.blog-card h3 { margin: 0 0 4px; }
.blog-card .blog-date { color: var(--muted); font-size: 0.8rem; margin-bottom: 6px; }
.blog-card p { margin: 0; color: var(--text); font-size: 0.92rem; }