#3974CB

CSS

:root {
  --fading-night: #3974cb;
  --fading-night-rgb: 57 116 203;
  --fading-night-oklch: oklch(0.564 0.148 258.2);
}

.element {
  color: var(--fading-night);
  background-color: hsl(216 58% 51%);
  border-color: oklch(0.564 0.148 258.2);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3974cb;
  --color-fading-night-50: #ddf7ff;
  --color-fading-night-100: #cce9ff;
  --color-fading-night-200: #b0d6ff;
  --color-fading-night-300: #8bb8ff;
  --color-fading-night-400: #659ff5;
  --color-fading-night-500: #4284e6;
  --color-fading-night-600: #3970c2;
  --color-fading-night-700: #2d5a9c;
  --color-fading-night-800: #1c4274;
  --color-fading-night-900: #122e52;
  --color-fading-night-950: #041a37;
}

SCSS

$fading-night: #3974cb;
$fading-night-rgb: 57, 116, 203;
$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);
}