#3037A8

CSS

:root {
  --depths-of-night: #3037a8;
  --depths-of-night-rgb: 48 55 168;
  --depths-of-night-oklch: oklch(0.41 0.178 272.8);
}

.element {
  color: var(--depths-of-night);
  background-color: hsl(237 56% 42%);
  border-color: oklch(0.41 0.178 272.8);
}

Tailwind CSS v4

@theme {
  --color-depths-of-night: #3037a8;
  --color-depths-of-night-50: #e6f2ff;
  --color-depths-of-night-100: #d6e4ff;
  --color-depths-of-night-200: #beceff;
  --color-depths-of-night-300: #9dafff;
  --color-depths-of-night-400: #7d94ff;
  --color-depths-of-night-500: #6276f9;
  --color-depths-of-night-600: #5365d2;
  --color-depths-of-night-700: #4250a9;
  --color-depths-of-night-800: #2c3b7f;
  --color-depths-of-night-900: #1e295a;
  --color-depths-of-night-950: #0e163d;
}

SCSS

$depths-of-night: #3037a8;
$depths-of-night-rgb: 48, 55, 168;
$depths-of-night-light: mix(#fff, $depths-of-night, 20%);
$depths-of-night-dark: mix(#000, $depths-of-night, 20%);

.element {
  color: $depths-of-night;
  box-shadow: 0 0 0 2px rgba($depths-of-night, 0.35);
}