#0B3D68

CSS

:root {
  --tardis-blue: #0b3d68;
  --tardis-blue-rgb: 11 61 104;
  --tardis-blue-oklch: oklch(0.353 0.09 249.8);
}

.element {
  color: var(--tardis-blue);
  background-color: hsl(208 81% 23%);
  border-color: oklch(0.353 0.09 249.8);
}

Tailwind CSS v4

@theme {
  --color-tardis-blue: #0b3d68;
  --color-tardis-blue-50: #e3f8ff;
  --color-tardis-blue-100: #d3ebff;
  --color-tardis-blue-200: #b9d8fa;
  --color-tardis-blue-300: #96bbe5;
  --color-tardis-blue-400: #75a3d2;
  --color-tardis-blue-500: #558ac0;
  --color-tardis-blue-600: #4975a2;
  --color-tardis-blue-700: #3a5e82;
  --color-tardis-blue-800: #284560;
  --color-tardis-blue-900: #1a3043;
  --color-tardis-blue-950: #0b1c2b;
}

SCSS

$tardis-blue: #0b3d68;
$tardis-blue-rgb: 11, 61, 104;
$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);
}