Dark Night

CSS

:root {
  --dark-night: #404b57;
  --dark-night-rgb: 64 75 87;
  --dark-night-oklch: oklch(0.408 0.025 250.7);
}

.element {
  color: var(--dark-night);
  background-color: hsl(211 15% 30%);
  border-color: oklch(0.408 0.025 250.7);
}

Tailwind CSS v4

@theme {
  --color-dark-night: #404b57;
  --color-dark-night-50: #f0f6fc;
  --color-dark-night-100: #e2e9f0;
  --color-dark-night-200: #cdd5df;
  --color-dark-night-300: #afb8c4;
  --color-dark-night-400: #94a0ad;
  --color-dark-night-500: #7a8896;
  --color-dark-night-600: #68737f;
  --color-dark-night-700: #535c66;
  --color-dark-night-800: #3c434b;
  --color-dark-night-900: #292e34;
  --color-dark-night-950: #171b1f;
}

SCSS

$dark-night: #404b57;
$dark-night-rgb: 64, 75, 87;
$dark-night-light: mix(#fff, $dark-night, 20%);
$dark-night-dark: mix(#000, $dark-night, 20%);

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