#3877CA

CSS

:root {
  --fading-night: #3877ca;
  --fading-night-rgb: 56 119 202;
  --fading-night-oklch: oklch(0.57 0.144 256.4);
}

.element {
  color: var(--fading-night);
  background-color: hsl(214 58% 51%);
  border-color: oklch(0.57 0.144 256.4);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3877ca;
  --color-fading-night-50: #dcf7ff;
  --color-fading-night-100: #cbeaff;
  --color-fading-night-200: #afd6ff;
  --color-fading-night-300: #89b9ff;
  --color-fading-night-400: #63a0f2;
  --color-fading-night-500: #3f86e3;
  --color-fading-night-600: #3671bf;
  --color-fading-night-700: #2b5b9a;
  --color-fading-night-800: #1a4373;
  --color-fading-night-900: #112e51;
  --color-fading-night-950: #041b36;
}

SCSS

$fading-night: #3877ca;
$fading-night-rgb: 56, 119, 202;
$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);
}