#3974C9

CSS

:root {
  --fading-night: #3974c9;
  --fading-night-rgb: 57 116 201;
  --fading-night-oklch: oklch(0.563 0.146 257.8);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 57% 51%);
  border-color: oklch(0.563 0.146 257.8);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3974c9;
  --color-fading-night-50: #ddf7ff;
  --color-fading-night-100: #cceaff;
  --color-fading-night-200: #b0d6ff;
  --color-fading-night-300: #8bb8ff;
  --color-fading-night-400: #669ff3;
  --color-fading-night-500: #4285e5;
  --color-fading-night-600: #3971c1;
  --color-fading-night-700: #2d5a9b;
  --color-fading-night-800: #1c4273;
  --color-fading-night-900: #122e51;
  --color-fading-night-950: #051a36;
}

SCSS

$fading-night: #3974c9;
$fading-night-rgb: 57, 116, 201;
$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);
}