#0040B0

CSS

:root {
  --once-in-a-blue-moon: #0040b0;
  --once-in-a-blue-moon-rgb: 0 64 176;
  --once-in-a-blue-moon-oklch: oklch(0.419 0.187 261.5);
}

.element {
  color: var(--once-in-a-blue-moon);
  background-color: hsl(218 100% 35%);
  border-color: oklch(0.419 0.187 261.5);
}

Tailwind CSS v4

@theme {
  --color-once-in-a-blue-moon: #0040b0;
  --color-once-in-a-blue-moon-50: #daf6ff;
  --color-once-in-a-blue-moon-100: #c8e8ff;
  --color-once-in-a-blue-moon-200: #abd4ff;
  --color-once-in-a-blue-moon-300: #85b5ff;
  --color-once-in-a-blue-moon-400: #5d9aff;
  --color-once-in-a-blue-moon-500: #387eff;
  --color-once-in-a-blue-moon-600: #316bd7;
  --color-once-in-a-blue-moon-700: #2756ad;
  --color-once-in-a-blue-moon-800: #153f82;
  --color-once-in-a-blue-moon-900: #0d2c5c;
  --color-once-in-a-blue-moon-950: #02183f;
}

SCSS

$once-in-a-blue-moon: #0040b0;
$once-in-a-blue-moon-rgb: 0, 64, 176;
$once-in-a-blue-moon-light: mix(#fff, $once-in-a-blue-moon, 20%);
$once-in-a-blue-moon-dark: mix(#000, $once-in-a-blue-moon, 20%);

.element {
  color: $once-in-a-blue-moon;
  box-shadow: 0 0 0 2px rgba($once-in-a-blue-moon, 0.35);
}