:root {
  /* Brand (slightly deeper blues & accents) */
  --bt-blue: #0044cc;            /* primary - deep royal blue */
  --bt-blue-100: #e6edff;        /* soft tint for backgrounds */
  --bt-orange: #e65528;          /* warm accent - burnt orange */

  /* Neutrals */
  --bt-bg: #ffffff;              /* page background */
  --bt-surface: #ffffff;         /* card background */
  --bt-ink: #35486e;             /* headings - richer than #0f172a */
  --bt-text: #333;            /* main body text - dark gray */
  --bt-muted: #4b5563;           /* muted text - mid gray */
  --bt-border: rgba(38, 41, 48, 0.12); /* subtle dark border */

  /* Radius */
  --bt-radius-sm: 12px;
  --bt-radius: 16px;
  --bt-radius-lg: 20px;

  /* Shadows (slightly stronger for white background contrast) */
  --bt-shadow: 0 4px 12px rgba(17, 24, 39, 0.08);
  --bt-shadow-lg: 0 10px 28px rgba(17, 24, 39, 0.14);

  /* Typography */
  --bt-font-sans: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, Inter, "Helvetica Neue", Arial;

  /* Motion */
  --bt-ease: cubic-bezier(.2,.7,.2,1);
  --bt-speed: .22s;
}

/* Optional dark mode: keep colors rich in light mode, invert for dark mode */
@media (prefers-color-scheme: dark) {
  :root {
    --bt-bg: #0b1220;
    --bt-surface: #0f172a;
    --bt-ink: #35486e;
    --bt-text: #333;
    --bt-muted: #9ca3af;
    --bt-border: rgba(255,255,255,0.12);
    --bt-shadow: 0 6px 20px rgba(0,0,0,0.35);
    --bt-shadow-lg: 0 12px 34px rgba(0,0,0,0.55);
  }
}