#3878C2

CSS

:root {
  --fading-night: #3878c2;
  --fading-night-rgb: 56 120 194;
  --fading-night-oklch: oklch(0.567 0.132 253.9);
}

.element {
  color: var(--fading-night);
  background-color: hsl(212 55% 49%);
  border-color: oklch(0.567 0.132 253.9);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3878c2;
  --color-fading-night-50: #ddf8ff;
  --color-fading-night-100: #cbebff;
  --color-fading-night-200: #afd7ff;
  --color-fading-night-300: #8abafa;
  --color-fading-night-400: #64a1eb;
  --color-fading-night-500: #4088db;
  --color-fading-night-600: #3773b9;
  --color-fading-night-700: #2c5c94;
  --color-fading-night-800: #1b446e;
  --color-fading-night-900: #122f4e;
  --color-fading-night-950: #041b34;
}

SCSS

$fading-night: #3878c2;
$fading-night-rgb: 56, 120, 194;
$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);
}