#3178C9

CSS

:root {
  --fading-night: #3178c9;
  --fading-night-rgb: 49 120 201;
  --fading-night-oklch: oklch(0.569 0.144 254.1);
}

.element {
  color: var(--fading-night);
  background-color: hsl(212 61% 49%);
  border-color: oklch(0.569 0.144 254.1);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3178c9;
  --color-fading-night-50: #dbf8ff;
  --color-fading-night-100: #c9ebff;
  --color-fading-night-200: #acd7ff;
  --color-fading-night-300: #86baff;
  --color-fading-night-400: #5ea1f1;
  --color-fading-night-500: #3787e2;
  --color-fading-night-600: #3073bf;
  --color-fading-night-700: #265c99;
  --color-fading-night-800: #164472;
  --color-fading-night-900: #0e2f50;
  --color-fading-night-950: #021b36;
}

SCSS

$fading-night: #3178c9;
$fading-night-rgb: 49, 120, 201;
$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);
}