:root {
  --bg: #f6f6f4;
  --card: #ffffff;
  --surface-alt: #eeede8;
  --border: #e2e1dc;
  --border-strong: #cfcdc5;
  --text: #1c1c1a;
  --text-secondary: #6b6a64;
  --text-faint: #a3a29b;
  --accent: #2f6fed;
  --accent-hover: #2559c4;
  --accent-soft: rgba(47, 111, 237, 0.14);
  --accent-soft-2: rgba(47, 111, 237, 0.32);
  --danger-bg: #fcebeb; --danger-text: #a32d2d;
  --warning-bg: #faeeda; --warning-text: #854f0b;
  --success-bg: #eaf3de; --success-text: #3b6d11;
  --radius: 10px;
  --radius-lg: 16px;
  --mono: "SF Mono", Consolas, Menlo, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #171715;
    --card: #232320;
    --surface-alt: #2a2a26;
    --border: #34342f;
    --border-strong: #46453d;
    --text: #f2f1ec;
    --text-secondary: #a5a49c;
    --text-faint: #6f6e66;
    --danger-bg: #3a1414; --danger-text: #f09595;
    --warning-bg: #3a2a08; --warning-text: #fac775;
    --success-bg: #1c2a10; --success-text: #97c459;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
}

/* Centered single-column layout, used by the simpler tool pages. */
body.centered {
  display: flex;
  justify-content: center;
  padding: 48px 20px;
}
.page {
  width: 100%;
  max-width: 480px;
}

/* Surface treatment shared by card-based pages. Padding is left to the page,
   since some cards (e.g. f1) lay out their own internal sections. */
.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
}
.card h1 { font-size: 18px; font-weight: 600; margin: 0 0 20px; }

.sub { color: var(--text-secondary); font-size: 13px; margin: 0 0 20px; }

.back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 13px;
  font-weight: 600;
  color: var(--text-secondary);
  text-decoration: none;
  margin-bottom: 16px;
}
.back-link:hover { color: var(--accent); }