:root {
  --bg: #ffffff; --fg: #1a1a2e; --muted: #5a5a72;
  --accent: #2563eb; --accent-dark: #1e40af;
  --card: #f4f6fb; --border: #e3e7f0; --ok: #16a34a; --radius: 12px;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: -apple-system, "Segoe UI", Roboto, sans-serif; color: var(--fg); background: var(--bg); line-height: 1.6; }
.site-header { display: flex; justify-content: space-between; align-items: center; padding: 16px 24px; border-bottom: 1px solid var(--border); }
.logo { font-weight: 700; font-size: 18px; color: var(--fg); text-decoration: none; }
nav a { margin-left: 20px; color: var(--muted); text-decoration: none; }
nav a:hover { color: var(--accent); }
main { max-width: 720px; margin: 0 auto; padding: 32px 20px 64px; }
.hero { text-align: center; margin: 24px 0; }
.hero h1 { font-size: 32px; margin-bottom: 8px; }
.sub { color: var(--muted); font-size: 17px; }
.tool-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 24px; margin: 24px 0; }
.field { margin-bottom: 14px; }
.field label { display: block; font-weight: 600; margin-bottom: 4px; font-size: 14px; }
.field input, .field select { width: 100%; padding: 10px 12px; border: 1px solid var(--border); border-radius: 8px; font-size: 16px; background: #fff; }
.btn { display: inline-block; background: var(--accent); color: #fff; border: none; border-radius: 8px; padding: 12px 24px; font-size: 16px; font-weight: 600; cursor: pointer; text-decoration: none; }
.btn:hover { background: var(--accent-dark); }
.result { margin-top: 16px; padding: 16px; background: #fff; border: 1px solid var(--border); border-radius: 8px; }
.result-main { font-size: 22px; font-weight: 700; color: var(--ok); }
.result-note { color: var(--muted); font-size: 13px; margin-top: 4px; }
.content h2 { margin: 28px 0 10px; font-size: 22px; }
.content h3 { margin: 18px 0 6px; font-size: 17px; }
.content code { background: var(--card); padding: 2px 8px; border-radius: 6px; font-size: 15px; }
.site-footer { border-top: 1px solid var(--border); padding: 20px 24px; text-align: center; color: var(--muted); font-size: 13px; }
@media (max-width: 480px) { .hero h1 { font-size: 26px; } main { padding: 20px 14px 48px; } }