#2B4867

CSS

:root {
  --stay-the-night: #2b4867;
  --stay-the-night-rgb: 43 72 103;
  --stay-the-night-oklch: oklch(0.394 0.063 251.2);
}

.element {
  color: var(--stay-the-night);
  background-color: hsl(211 41% 29%);
  border-color: oklch(0.394 0.063 251.2);
}

Tailwind CSS v4

@theme {
  --color-stay-the-night: #2b4867;
  --color-stay-the-night-50: #e9f7ff;
  --color-stay-the-night-100: #daeafd;
  --color-stay-the-night-200: #c2d6ef;
  --color-stay-the-night-300: #a1bad8;
  --color-stay-the-night-400: #83a2c3;
  --color-stay-the-night-500: #6789af;
  --color-stay-the-night-600: #577494;
  --color-stay-the-night-700: #465d77;
  --color-stay-the-night-800: #314458;
  --color-stay-the-night-900: #212f3d;
  --color-stay-the-night-950: #111c27;
}

SCSS

$stay-the-night: #2b4867;
$stay-the-night-rgb: 43, 72, 103;
$stay-the-night-light: mix(#fff, $stay-the-night, 20%);
$stay-the-night-dark: mix(#000, $stay-the-night, 20%);

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