#3175CA

CSS

:root {
  --fading-night: #3175ca;
  --fading-night-rgb: 49 117 202;
  --fading-night-oklch: oklch(0.563 0.148 255.7);
}

.element {
  color: var(--fading-night);
  background-color: hsl(213 61% 49%);
  border-color: oklch(0.563 0.148 255.7);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3175ca;
  --color-fading-night-50: #dbf7ff;
  --color-fading-night-100: #c9eaff;
  --color-fading-night-200: #add7ff;
  --color-fading-night-300: #87b9ff;
  --color-fading-night-400: #60a0f4;
  --color-fading-night-500: #3986e6;
  --color-fading-night-600: #3271c2;
  --color-fading-night-700: #285b9c;
  --color-fading-night-800: #174374;
  --color-fading-night-900: #0f2e52;
  --color-fading-night-950: #021b37;
}

SCSS

$fading-night: #3175ca;
$fading-night-rgb: 49, 117, 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);
}