#1F3442

CSS

:root {
  --blue-whale: #1f3442;
  --blue-whale-rgb: 31 52 66;
  --blue-whale-oklch: oklch(0.314 0.037 238.7);
}

.element {
  color: var(--blue-whale);
  background-color: hsl(204 36% 19%);
  border-color: oklch(0.314 0.037 238.7);
}

Tailwind CSS v4

@theme {
  --color-blue-whale: #1f3442;
  --color-blue-whale-50: #ecf7ff;
  --color-blue-whale-100: #ddeaf3;
  --color-blue-whale-200: #c7d7e3;
  --color-blue-whale-300: #a7bac9;
  --color-blue-whale-400: #8ba2b2;
  --color-blue-whale-500: #708a9c;
  --color-blue-whale-600: #5f7584;
  --color-blue-whale-700: #4c5d6a;
  --color-blue-whale-800: #36454e;
  --color-blue-whale-900: #252f36;
  --color-blue-whale-950: #141c21;
}

SCSS

$blue-whale: #1f3442;
$blue-whale-rgb: 31, 52, 66;
$blue-whale-light: mix(#fff, $blue-whale, 20%);
$blue-whale-dark: mix(#000, $blue-whale, 20%);

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