#4178BD

CSS

:root {
  --fading-night: #4178bd;
  --fading-night-rgb: 65 120 189;
  --fading-night-oklch: oklch(0.568 0.122 255.1);
}

.element {
  color: var(--fading-night);
  background-color: hsl(213 49% 50%);
  border-color: oklch(0.568 0.122 255.1);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #4178bd;
  --color-fading-night-50: #dff7ff;
  --color-fading-night-100: #cfeaff;
  --color-fading-night-200: #b3d7ff;
  --color-fading-night-300: #8fbaf6;
  --color-fading-night-400: #6ba1e5;
  --color-fading-night-500: #4a88d5;
  --color-fading-night-600: #3f73b4;
  --color-fading-night-700: #325c90;
  --color-fading-night-800: #21446b;
  --color-fading-night-900: #162f4c;
  --color-fading-night-950: #071b32;
}

SCSS

$fading-night: #4178bd;
$fading-night-rgb: 65, 120, 189;
$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);
}