#3B75CE

CSS

:root {
  --fading-night: #3b75ce;
  --fading-night-rgb: 59 117 206;
  --fading-night-oklch: oklch(0.569 0.15 258.8);
}

.element {
  color: var(--fading-night);
  background-color: hsl(216 60% 52%);
  border-color: oklch(0.569 0.15 258.8);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3b75ce;
  --color-fading-night-50: #ddf7ff;
  --color-fading-night-100: #cce9ff;
  --color-fading-night-200: #b0d5ff;
  --color-fading-night-300: #8bb8ff;
  --color-fading-night-400: #659ef6;
  --color-fading-night-500: #4284e8;
  --color-fading-night-600: #3970c3;
  --color-fading-night-700: #2d599d;
  --color-fading-night-800: #1c4275;
  --color-fading-night-900: #122e53;
  --color-fading-night-950: #051a37;
}

SCSS

$fading-night: #3b75ce;
$fading-night-rgb: 59, 117, 206;
$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);
}