#3975D3

CSS

:root {
  --fading-night: #3975d3;
  --fading-night-rgb: 57 117 211;
  --fading-night-oklch: oklch(0.572 0.158 259.2);
}

.element {
  color: var(--fading-night);
  background-color: hsl(217 64% 53%);
  border-color: oklch(0.572 0.158 259.2);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3975d3;
  --color-fading-night-50: #dcf6ff;
  --color-fading-night-100: #cbe9ff;
  --color-fading-night-200: #aed5ff;
  --color-fading-night-300: #89b7ff;
  --color-fading-night-400: #639efa;
  --color-fading-night-500: #3f83ec;
  --color-fading-night-600: #376fc7;
  --color-fading-night-700: #2b59a0;
  --color-fading-night-800: #1a4278;
  --color-fading-night-900: #112d54;
  --color-fading-night-950: #041a39;
}

SCSS

$fading-night: #3975d3;
$fading-night-rgb: 57, 117, 211;
$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);
}