#2878CB

CSS

:root {
  --fading-night: #2878cb;
  --fading-night-rgb: 40 120 203;
  --fading-night-oklch: oklch(0.568 0.149 252.8);
}

.element {
  color: var(--fading-night);
  background-color: hsl(211 67% 48%);
  border-color: oklch(0.568 0.149 252.8);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #2878cb;
  --color-fading-night-50: #d9f8ff;
  --color-fading-night-100: #c7ebff;
  --color-fading-night-200: #a9d8ff;
  --color-fading-night-300: #82bbff;
  --color-fading-night-400: #59a2f4;
  --color-fading-night-500: #2d88e5;
  --color-fading-night-600: #2873c1;
  --color-fading-night-700: #205c9b;
  --color-fading-night-800: #104474;
  --color-fading-night-900: #0a2f51;
  --color-fading-night-950: #001b36;
}

SCSS

$fading-night: #2878cb;
$fading-night-rgb: 40, 120, 203;
$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);
}