:root {
  --bg: #0f172a;
  --card: #1e293b;
  --border: #334155;
  --text: #f8fafc;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --radius: 8px;
}

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

.container {
  max-width: 860px;
  margin: 0 auto;
  padding: 40px 20px;
}

.block { margin: 32px 0; padding: 24px; background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); }
.block h2 { font-size: 1.15rem; text-transform: uppercase; letter-spacing: .08em; color: var(--accent); margin-bottom: 16px; margin-top: 0; }

.factor-matrix { width: 100%; border-collapse: collapse; font-family: ui-monospace, monospace; font-size: .9rem; }
.factor-matrix th { text-align: left; padding: 10px; border-bottom: 2px solid var(--border); color: var(--muted); font-weight: 600; }
.factor-matrix td { padding: 10px; border-bottom: 1px solid var(--border); }
.factor-matrix code { background: var(--bg); padding: 2px 6px; border-radius: 4px; color: var(--accent); }

.derivation-steps { list-style: decimal; padding-left: 24px; }
.derivation-steps li { margin: 8px 0; }
.derivation-steps code { background: var(--bg); padding: 4px 8px; border-radius: 4px; font-size: .85rem; }

.dimension-check { margin-top: 12px; color: var(--muted); font-size: .9rem; }

.precision-note { margin-top: 12px; font-size: .75rem; color: var(--muted); text-align: center; letter-spacing: .05em; text-transform: uppercase; }

.references { list-style: decimal; padding-left: 24px; font-size: .9rem; }
.references li { margin: 6px 0; color: var(--muted); }
.references cite { color: var(--text); font-style: normal; font-weight: 600; }
.references a { color: var(--accent); text-decoration: none; }
.references a:hover { text-decoration: underline; }

.categories {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 16px;
  margin: 32px 0;
}
.categories a {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 16px;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  text-decoration: none;
  color: var(--text);
  transition: border-color 0.15s ease, transform 0.15s ease;
}
.categories a:hover {
  border-color: var(--accent);
}
.categories .icon {
  font-size: 1.5rem;
}
.categories .name {
  font-weight: 600;
  font-size: 1rem;
}

.muted { color: var(--muted); font-size: .85rem; }

/* Interactive Converter Styling */
.converter-widget {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
}
.converter-grid {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 16px;
  align-items: center;
}
.field {
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.field label {
  font-size: 0.85rem;
  color: var(--muted);
  font-weight: 500;
}
.field input, .field select {
  background: var(--card);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 10px 14px;
  border-radius: 6px;
  font-size: 1rem;
  font-family: ui-monospace, monospace;
}
.field input:focus, .field select:focus {
  outline: 2px solid var(--accent);
  border-color: transparent;
}
.swap-btn {
  background: var(--card);
  border: 1px solid var(--border);
  color: var(--accent);
  font-size: 1.25rem;
  padding: 8px 12px;
  border-radius: 6px;
  cursor: pointer;
  transition: background 0.15s ease;
  align-self: flex-end;
  margin-bottom: 2px;
}
.swap-btn:hover {
  background: var(--border);
}
.result {
  margin-top: 20px;
  text-align: center;
  padding-top: 16px;
  border-top: 1px solid var(--border);
}
.result .value {
  font-size: 1.75rem;
  font-weight: 700;
  color: var(--accent);
  font-family: ui-monospace, monospace;
}
.result .formula {
  font-size: 0.85rem;
  color: var(--muted);
  margin-top: 4px;
}

/* Hero Section & Quick Links */
.hero { text-align: center; padding: 32px 0; }
.hero h1 { font-size: 2.2rem; margin-bottom: 12px; }
.hero-sub { color: var(--muted); max-width: 640px; margin: 0 auto 24px; }
.hero-calculator { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 24px; max-width: 720px; margin: 0 auto; }
.quick-links { margin-top: 20px; color: var(--muted); }
.quick-links a { color: var(--accent); }
.hero-secondary { margin-top: 12px; font-size: .9rem; color: var(--muted); }
.hero-secondary a { color: var(--accent); }