#3972D1

CSS

:root {
  --fading-night: #3972d1;
  --fading-night-rgb: 57 114 209;
  --fading-night-oklch: oklch(0.564 0.159 260);
}

.element {
  color: var(--fading-night);
  background-color: hsl(218 62% 52%);
  border-color: oklch(0.564 0.159 260);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3972d1;
  --color-fading-night-50: #ddf6ff;
  --color-fading-night-100: #cbe9ff;
  --color-fading-night-200: #afd5ff;
  --color-fading-night-300: #8ab7ff;
  --color-fading-night-400: #659dfb;
  --color-fading-night-500: #4282ed;
  --color-fading-night-600: #396ec8;
  --color-fading-night-700: #2d58a1;
  --color-fading-night-800: #1b4178;
  --color-fading-night-900: #122d55;
  --color-fading-night-950: #041939;
}

SCSS

$fading-night: #3972d1;
$fading-night-rgb: 57, 114, 209;
$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);
}