#3575D4

CSS

:root {
  --fading-night: #3575d4;
  --fading-night-rgb: 53 117 212;
  --fading-night-oklch: oklch(0.571 0.16 258.4);
}

.element {
  color: var(--fading-night);
  background-color: hsl(216 65% 52%);
  border-color: oklch(0.571 0.16 258.4);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3575d4;
  --color-fading-night-50: #dbf7ff;
  --color-fading-night-100: #c9e9ff;
  --color-fading-night-200: #add5ff;
  --color-fading-night-300: #87b8ff;
  --color-fading-night-400: #609efc;
  --color-fading-night-500: #3b83ee;
  --color-fading-night-600: #336fc9;
  --color-fading-night-700: #2959a1;
  --color-fading-night-800: #184278;
  --color-fading-night-900: #0f2d55;
  --color-fading-night-950: #031a39;
}

SCSS

$fading-night: #3575d4;
$fading-night-rgb: 53, 117, 212;
$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);
}