#3574D6

CSS

:root {
  --fading-night: #3574d6;
  --fading-night-rgb: 53 116 214;
  --fading-night-oklch: oklch(0.57 0.164 259.1);
}

.element {
  color: var(--fading-night);
  background-color: hsl(217 66% 52%);
  border-color: oklch(0.57 0.164 259.1);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3574d6;
  --color-fading-night-50: #dbf7ff;
  --color-fading-night-100: #c9e9ff;
  --color-fading-night-200: #add5ff;
  --color-fading-night-300: #87b7ff;
  --color-fading-night-400: #609dfe;
  --color-fading-night-500: #3b82f0;
  --color-fading-night-600: #336fcb;
  --color-fading-night-700: #2958a3;
  --color-fading-night-800: #18417a;
  --color-fading-night-900: #0f2d56;
  --color-fading-night-950: #03193a;
}

SCSS

$fading-night: #3574d6;
$fading-night-rgb: 53, 116, 214;
$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);
}