#3774D5

CSS

:root {
  --fading-night: #3774d5;
  --fading-night-rgb: 55 116 213;
  --fading-night-oklch: oklch(0.57 0.162 259.4);
}

.element {
  color: var(--fading-night);
  background-color: hsl(217 65% 53%);
  border-color: oklch(0.57 0.162 259.4);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3774d5;
  --color-fading-night-50: #dcf6ff;
  --color-fading-night-100: #cae9ff;
  --color-fading-night-200: #aed5ff;
  --color-fading-night-300: #88b7ff;
  --color-fading-night-400: #629dfd;
  --color-fading-night-500: #3e82ef;
  --color-fading-night-600: #356fca;
  --color-fading-night-700: #2a58a2;
  --color-fading-night-800: #194179;
  --color-fading-night-900: #102d56;
  --color-fading-night-950: #03193a;
}

SCSS

$fading-night: #3774d5;
$fading-night-rgb: 55, 116, 213;
$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);
}