:root {
  --bg: #0f1115;
  --surface: #171a21;
  --text: #e8e8ec;
  --muted: #9aa0ab;
  --accent: #4fd8c4;
  --border: #262b35;
}

* { box-sizing: border-box; }

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

.site-header {
  padding: 3rem 1.5rem 2rem;
  text-align: center;
}

.site-header h1 {
  margin: 0 0 0.5rem;
  font-size: 2rem;
}

.badge {
  font-size: 0.9rem;
  color: var(--muted);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.1rem 0.6rem;
  margin-left: 0.5rem;
  vertical-align: middle;
}

.tagline {
  color: var(--muted);
  max-width: 40rem;
  margin: 0 auto;
}

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1.25rem;
  max-width: 60rem;
  margin: 0 auto;
  padding: 1rem 1.5rem 3rem;
}

.card {
  display: block;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.5rem;
  text-decoration: none;
  color: var(--text);
  transition: border-color 0.15s ease, transform 0.15s ease;
}

.card:hover {
  border-color: var(--accent);
  transform: translateY(-2px);
}

.card h2 {
  margin: 0 0 0.5rem;
  font-size: 1.15rem;
}

.card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}

.status {
  display: inline-block;
  margin-top: 1rem;
  font-size: 0.75rem;
  color: var(--accent);
  border: 1px solid currentColor;
  border-radius: 999px;
  padding: 0.1rem 0.6rem;
}

.site-footer {
  text-align: center;
  color: var(--muted);
  padding: 2rem 1.5rem 3rem;
  font-size: 0.85rem;
}

.page {
  max-width: 40rem;
  margin: 0 auto;
  padding: 3rem 1.5rem;
}

.page a.back {
  color: var(--accent);
  text-decoration: none;
}

.page h2 {
  font-size: 1.2rem;
  margin: 2rem 0 0.75rem;
}

.page p {
  color: var(--muted);
}

.page a {
  color: var(--accent);
}

.page-meta {
  margin-top: 3rem;
  font-size: 0.8rem;
  color: var(--muted);
}

.page-wide {
  max-width: 64rem;
}

.page-lede {
  color: var(--muted);
  margin-top: -0.5rem;
}

.tab-switch {
  display: flex;
  gap: 0.5rem;
  margin: 1.5rem 0;
}

.tab-btn {
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--muted);
  border-radius: 999px;
  padding: 0.5rem 1.25rem;
  font-size: 0.9rem;
  font-family: inherit;
  cursor: pointer;
}

.tab-btn.is-active {
  border-color: var(--accent);
  color: var(--text);
}

.cat-alkali { --cat: hsl(4, 70%, 68%); }
.cat-alkaline-earth { --cat: hsl(28, 70%, 65%); }
.cat-transition { --cat: hsl(45, 75%, 62%); }
.cat-lanthanide { --cat: hsl(80, 45%, 62%); }
.cat-actinide { --cat: hsl(110, 40%, 60%); }
.cat-post-transition { --cat: hsl(150, 40%, 58%); }
.cat-metalloid { --cat: hsl(172, 45%, 55%); }
.cat-nonmetal { --cat: hsl(200, 65%, 68%); }
.cat-halogen { --cat: hsl(230, 60%, 74%); }
.cat-noble-gas { --cat: hsl(285, 50%, 74%); }

.periodic-table {
  display: grid;
  grid-template-columns: repeat(18, minmax(28px, 1fr));
  grid-auto-rows: minmax(30px, 1fr);
  gap: 3px;
  overflow-x: auto;
  padding-bottom: 0.5rem;
}

.el-cell {
  background: color-mix(in srgb, var(--cat) 22%, var(--surface));
  border: 1px solid color-mix(in srgb, var(--cat) 55%, var(--border));
  border-radius: 4px;
  color: var(--text);
  cursor: pointer;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 2px;
  font-family: inherit;
  min-width: 0;
}

.el-cell:hover {
  border-color: var(--cat);
  background: color-mix(in srgb, var(--cat) 40%, var(--surface));
}

.el-num {
  font-size: 0.5rem;
  color: var(--muted);
  line-height: 1;
}

.el-sym {
  font-size: 0.85rem;
  font-weight: 600;
  line-height: 1.2;
}

.el-mark {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.55rem;
  color: var(--muted);
  border: 1px dashed var(--border);
  border-radius: 4px;
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem 1rem;
  margin: 1rem 0;
  font-size: 0.8rem;
  color: var(--muted);
  padding: 0;
  list-style: none;
}

.legend-item {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
}

.legend-swatch {
  width: 0.7rem;
  height: 0.7rem;
  border-radius: 3px;
  background: var(--cat);
  display: inline-block;
}

.element-detail {
  display: flex;
  align-items: center;
  gap: 1rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.25rem;
  min-height: 4rem;
  color: var(--muted);
}

.detail-sym {
  font-size: 2rem;
  font-weight: 700;
  color: var(--cat);
  min-width: 3rem;
  text-align: center;
}

.detail-info {
  color: var(--text);
  line-height: 1.5;
}

.quiz-controls {
  display: flex;
  gap: 1.5rem;
  margin-bottom: 1rem;
  font-size: 0.9rem;
  color: var(--muted);
}

.quiz-score {
  color: var(--accent);
  font-weight: 600;
  margin-bottom: 1rem;
}

.quiz-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 2rem;
  text-align: center;
}

.quiz-question {
  font-size: 1.25rem;
  margin-bottom: 1.5rem;
}

.quiz-symbol {
  color: var(--accent);
  font-weight: 700;
  font-size: 1.6rem;
}

.quiz-choices {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: 0.75rem;
  margin-bottom: 1.5rem;
}

.quiz-choice {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.75rem;
  color: var(--text);
  font-size: 1rem;
  font-family: inherit;
  cursor: pointer;
}

.quiz-choice:hover:not(:disabled) {
  border-color: var(--accent);
}

.quiz-choice:disabled {
  cursor: default;
}

.quiz-choice.is-correct {
  border-color: #63e6be;
  background: rgba(99, 230, 190, 0.15);
  color: #63e6be;
}

.quiz-choice.is-wrong {
  border-color: #ff8787;
  background: rgba(255, 135, 135, 0.15);
  color: #ff8787;
}

.quiz-next {
  background: var(--accent);
  color: var(--bg);
  border: none;
  border-radius: 999px;
  padding: 0.6rem 1.5rem;
  font-size: 0.95rem;
  font-family: inherit;
  cursor: pointer;
}