#4275BF

CSS

:root {
  --fading-night: #4275bf;
  --fading-night-rgb: 66 117 191;
  --fading-night-oklch: oklch(0.563 0.128 257.8);
}

.element {
  color: var(--fading-night);
  background-color: hsl(216 49% 50%);
  border-color: oklch(0.563 0.128 257.8);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #4275bf;
  --color-fading-night-50: #e0f7ff;
  --color-fading-night-100: #cfe9ff;
  --color-fading-night-200: #b4d6ff;
  --color-fading-night-300: #91b9f9;
  --color-fading-night-400: #6da0e9;
  --color-fading-night-500: #4c86d9;
  --color-fading-night-600: #4172b7;
  --color-fading-night-700: #345b93;
  --color-fading-night-800: #22436e;
  --color-fading-night-900: #162e4d;
  --color-fading-night-950: #081b33;
}

SCSS

$fading-night: #4275bf;
$fading-night-rgb: 66, 117, 191;
$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);
}