#3377CD

CSS

:root {
  --fading-night: #3377cd;
  --fading-night-rgb: 51 119 205;
  --fading-night-oklch: oklch(0.57 0.149 255.9);
}

.element {
  color: var(--fading-night);
  background-color: hsl(214 61% 50%);
  border-color: oklch(0.57 0.149 255.9);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3377cd;
  --color-fading-night-50: #dbf7ff;
  --color-fading-night-100: #c9eaff;
  --color-fading-night-200: #acd7ff;
  --color-fading-night-300: #87b9ff;
  --color-fading-night-400: #5fa0f5;
  --color-fading-night-500: #3986e6;
  --color-fading-night-600: #3271c2;
  --color-fading-night-700: #275b9c;
  --color-fading-night-800: #174374;
  --color-fading-night-900: #0f2e52;
  --color-fading-night-950: #021b37;
}

SCSS

$fading-night: #3377cd;
$fading-night-rgb: 51, 119, 205;
$fading-night-light: mix(#fff, $fading-night, 20%);
$fading-night-dark: mix(#000, $fading-night, 20%);

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