:root {
  --primary: #3b82f6;
  --primary-hover: #2563eb;
  --bg: #f4f7fb;
  --card: #ffffff;
  --text: #0f172a;
  --muted: #64748b;
  --border: #e5e7eb;
  --radius: 10px;
  color-scheme: light dark;
}
.dark {
  --primary: #60a5fa;
  --primary-hover: #3b82f6;
  --bg: #0b1220;
  --card: #0f172a;
  --text: #e5e7eb;
  --muted: #93a4b7;
  --border: #1f2937;
}
* { box-sizing: border-box; }
body {
  font-family: Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  padding: 24px;
  transition: background 0.2s ease, color 0.2s ease;
}
.converter {
  background: var(--card);
  max-width: 820px;
  margin: auto;
  padding: 22px;
  border-radius: var(--radius);
  box-shadow: 0 4px 18px rgba(0, 0, 0, 0.08);
  border: 1px solid var(--border);
}
.topbar { display: flex; justify-content: flex-end; gap: 10px; }
.theme-toggle {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 8px;
  height: 36px;
  padding: 6px 10px;
  cursor: pointer;
}
h1 { text-align: center; margin: 6px 0 16px; }
.sub {
  text-align: center;
  color: var(--muted);
  font-size: 14px;
  margin-top: -6px;
  margin-bottom: 18px;
}
label { display: block; margin-top: 12px; font-weight: 600; }
select,
input[type="number"] {
  width: 100%;
  padding: 10px 12px;
  margin-top: 6px;
  border: 1px solid var(--border);
  border-radius: 8px;
  height: 44px;
  font-size: 16px;
  background: var(--card);
  color: var(--text);
}
.grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.actions { display: grid; grid-template-columns: 1fr auto auto; gap: 10px; align-items: center; margin-top: 14px; }
button {
  padding: 10px 14px;
  border: none;
  border-radius: 8px;
  background: var(--primary);
  color: #fff;
  font-size: 16px;
  cursor: pointer;
  height: 44px;
}
button:hover { background: var(--primary-hover); }
.secondary { background: rgba(99, 102, 241, 0.12); color: var(--text); border: 1px solid var(--border); }
.secondary:hover { filter: brightness(0.95); }
.muted { background: #e5e7eb; color: #111; }
.dark .muted { background: #1f2937; color: #e5e7eb; }
.muted:hover { filter: brightness(0.95); }
.result { margin-top: 16px; font-size: 18px; font-weight: bold; text-align: center; min-height: 24px; }
.hint { text-align: center; color: var(--muted); font-size: 12px; }
.about { max-width: 820px; margin: 18px auto 0; color: var(--muted); font-size: 14px; line-height: 1.6; }
.site-footer { text-align: center; margin: 24px 0; color: var(--muted); }
.site-footer a { color: var(--primary); text-decoration: none; }
.site-footer a:hover { text-decoration: underline; }
button:disabled { opacity: .5; cursor: not-allowed; }