:root {
  --bg: #f3f5f9;
  --card: #ffffff;
  --text: #1d2433;
  --muted: #6b7489;
  --border: #d9deea;
  --accent: #3b6df0;
  --accent-soft: #e8eefe;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #12151c;
    --card: #1b2029;
    --text: #e6e9f0;
    --muted: #939bb0;
    --border: #2e3544;
    --accent: #6b93ff;
    --accent-soft: #232c45;
  }
}
* { box-sizing: border-box; }
body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 16px;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.5 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}
.card {
  width: 100%;
  max-width: 480px;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 24px;
  box-shadow: 0 4px 20px rgba(0,0,0,.06);
}
h1 { margin: 0 0 16px; font-size: 1.4rem; }
.tabs { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 20px; }
.tabs button {
  border: 1px solid var(--border);
  background: transparent;
  color: var(--muted);
  padding: 6px 12px;
  border-radius: 999px;
  font: inherit;
  font-size: .9rem;
  cursor: pointer;
}
.tabs button[aria-pressed="true"] {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}
.row { display: flex; gap: 8px; margin-bottom: 12px; }
input, select {
  font: inherit;
  color: var(--text);
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px 12px;
  min-width: 0;
}
input { flex: 1; }
select { flex: 0 0 42%; }
input:focus, select:focus, .tabs button:focus-visible, #swap:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 1px;
}
#swap {
  display: block;
  margin: 0 auto 12px;
  background: none;
  border: 1px solid var(--border);
  color: var(--accent);
  border-radius: 8px;
  padding: 4px 14px;
  font-size: 1rem;
  cursor: pointer;
}
#formula { margin: 16px 0 0; font-size: .85rem; color: var(--muted); text-align: center; }
.site-footer { margin-top: 16px; font-size: .8rem; color: var(--muted); text-align: center; }