#123D6B

CSS

:root {
  --tardis-blue: #123d6b;
  --tardis-blue-rgb: 18 61 107;
  --tardis-blue-oklch: oklch(0.357 0.092 253.2);
}

.element {
  color: var(--tardis-blue);
  background-color: hsl(211 71% 25%);
  border-color: oklch(0.357 0.092 253.2);
}

Tailwind CSS v4

@theme {
  --color-tardis-blue: #123d6b;
  --color-tardis-blue-50: #e4f7ff;
  --color-tardis-blue-100: #d4eaff;
  --color-tardis-blue-200: #bad7fc;
  --color-tardis-blue-300: #98bae7;
  --color-tardis-blue-400: #77a2d4;
  --color-tardis-blue-500: #5889c2;
  --color-tardis-blue-600: #4b74a4;
  --color-tardis-blue-700: #3c5d83;
  --color-tardis-blue-800: #294461;
  --color-tardis-blue-900: #1c2f44;
  --color-tardis-blue-950: #0c1c2c;
}

SCSS

$tardis-blue: #123d6b;
$tardis-blue-rgb: 18, 61, 107;
$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);
}