:root {
  --bg: #0f1420;
  --fg: #e8ecf3;
  --muted: #9aa5b8;
  --accent: #4da3ff;
  --card: #171e2e;
  --border: #263049;
  --radius: 10px;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--fg);
  line-height: 1.55;
}
.container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.site-header {
  border-bottom: 1px solid var(--border);
  background: var(--card);
}
.site-header .container {
  display: flex; align-items: center; justify-content: space-between; height: 60px;
}
.brand { font-weight: 700; font-size: 1.1rem; color: var(--fg); }
.site-header nav a { margin-left: 18px; color: var(--muted); }

.hero { padding: 48px 0 24px; }
.hero h1 { margin: 0 0 8px; font-size: 2rem; }
.hero p { color: var(--muted); margin: 0; font-size: 1.1rem; }

#tools h2 { margin-top: 40px; }
.tool-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 16px;
  margin: 20px 0 40px;
}
.tool-card {
  display: block;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
  color: var(--fg);
  transition: border-color .15s, transform .15s;
}
.tool-card:hover { border-color: var(--accent); transform: translateY(-2px); text-decoration: none; }
.tool-card h3 { margin: 0 0 6px; font-size: 1.02rem; }
.tool-card p { margin: 0; color: var(--muted); font-size: .9rem; }

/* calculator page */
.tool-page h1 { margin: 32px 0 4px; }
.tool-page .lead { color: var(--muted); margin: 0 0 24px; }

/* 3-column calculator layout: nav | schematic | values+result */
.calc-layout {
  display: grid;
  grid-template-columns: 210px 1fr 280px;
  gap: 16px;
  align-items: start;
  margin-bottom: 24px;
}

/* left: calculator navigator */
.calc-nav nav {
  display: flex;
  flex-direction: column;
  gap: 4px;
}
.calc-nav nav a {
  color: var(--muted);
  font-size: .92rem;
  padding: 6px 9px;
  border-radius: 6px;
  border: 1px solid transparent;
}
.calc-nav nav a:hover {
  color: var(--fg);
  background: var(--bg);
  text-decoration: none;
}
.calc-nav nav a.active {
  color: var(--accent);
  background: var(--bg);
  border-color: var(--border);
  font-weight: 600;
}
.calc-nav-home {
  display: block;
  margin-top: 14px;
  font-size: .88rem;
  color: var(--muted);
}
.calc-panel {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
}
.calc-panel h3 {
  margin: 0 0 12px;
  font-size: .72rem;
  text-transform: uppercase;
  letter-spacing: .1em;
  color: var(--muted);
}
.calc-schematic {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 260px;
}
.calc-schematic svg {
  width: 100%;
  max-width: 420px;
  height: auto;
}
@media (max-width: 900px) {
  .calc-layout { grid-template-columns: 1fr; }
}

.calc label { display: block; margin: 12px 0 4px; font-weight: 600; font-size: .92rem; }
.calc input[type="number"], .calc select {
  width: 100%; padding: 9px 11px;
  background: var(--bg); color: var(--fg);
  border: 1px solid var(--border); border-radius: 7px;
  font-size: 1rem;
}
.calc-panel .result {
  margin-top: 4px; padding: 14px;
  background: var(--bg); border: 1px solid var(--border);
  border-radius: 7px; font-size: 1.05rem;
}
.calc-panel .result strong { color: var(--accent); }
.explanation { color: var(--muted); }
.explanation h2 { color: var(--fg); font-size: 1.15rem; }

.site-footer {
  border-top: 1px solid var(--border);
  margin-top: 60px; padding: 20px 0;
  color: var(--muted); font-size: .88rem;
}
.site-footer .container { display: flex; justify-content: space-between; align-items: center; flex-wrap: wrap; gap: 8px; }
.site-footer nav a { margin-left: 16px; color: var(--muted); }

@media (max-width: 600px) {
  .hero { padding: 28px 0 12px; }
  .hero h1 { font-size: 1.5rem; }
}