#3B75C3

CSS

:root {
  --fading-night: #3b75c3;
  --fading-night-rgb: 59 117 195;
  --fading-night-oklch: oklch(0.562 0.136 256.6);
}

.element {
  color: var(--fading-night);
  background-color: hsl(214 54% 50%);
  border-color: oklch(0.562 0.136 256.6);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3b75c3;
  --color-fading-night-50: #def7ff;
  --color-fading-night-100: #cdeaff;
  --color-fading-night-200: #b1d6ff;
  --color-fading-night-300: #8cb9fd;
  --color-fading-night-400: #68a0ed;
  --color-fading-night-500: #4586de;
  --color-fading-night-600: #3b72bb;
  --color-fading-night-700: #2f5b97;
  --color-fading-night-800: #1e4370;
  --color-fading-night-900: #132e4f;
  --color-fading-night-950: #051b35;
}

SCSS

$fading-night: #3b75c3;
$fading-night-rgb: 59, 117, 195;
$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);
}