#3575C5

CSS

:root {
  --fading-night: #3575c5;
  --fading-night-rgb: 53 117 197;
  --fading-night-oklch: oklch(0.561 0.14 255.5);
}

.element {
  color: var(--fading-night);
  background-color: hsl(213 58% 49%);
  border-color: oklch(0.561 0.14 255.5);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3575c5;
  --color-fading-night-50: #dcf7ff;
  --color-fading-night-100: #cbeaff;
  --color-fading-night-200: #afd7ff;
  --color-fading-night-300: #89b9ff;
  --color-fading-night-400: #63a0f0;
  --color-fading-night-500: #3e86e1;
  --color-fading-night-600: #3672bd;
  --color-fading-night-700: #2b5b98;
  --color-fading-night-800: #1a4371;
  --color-fading-night-900: #112f50;
  --color-fading-night-950: #041b35;
}

SCSS

$fading-night: #3575c5;
$fading-night-rgb: 53, 117, 197;
$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);
}