#123C69

CSS

:root {
  --tardis-blue: #123c69;
  --tardis-blue-rgb: 18 60 105;
  --tardis-blue-oklch: oklch(0.353 0.091 253.2);
}

.element {
  color: var(--tardis-blue);
  background-color: hsl(211 71% 24%);
  border-color: oklch(0.353 0.091 253.2);
}

Tailwind CSS v4

@theme {
  --color-tardis-blue: #123c69;
  --color-tardis-blue-50: #e4f7ff;
  --color-tardis-blue-100: #d4eaff;
  --color-tardis-blue-200: #bbd7fb;
  --color-tardis-blue-300: #99bae6;
  --color-tardis-blue-400: #78a2d3;
  --color-tardis-blue-500: #5989c1;
  --color-tardis-blue-600: #4c74a3;
  --color-tardis-blue-700: #3d5d83;
  --color-tardis-blue-800: #2a4461;
  --color-tardis-blue-900: #1c2f44;
  --color-tardis-blue-950: #0c1c2c;
}

SCSS

$tardis-blue: #123c69;
$tardis-blue-rgb: 18, 60, 105;
$tardis-blue-light: mix(#fff, $tardis-blue, 20%);
$tardis-blue-dark: mix(#000, $tardis-blue, 20%);

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