#3F75BF

CSS

:root {
  --fading-night: #3f75bf;
  --fading-night-rgb: 63 117 191;
  --fading-night-oklch: oklch(0.561 0.129 256.8);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 50% 50%);
  border-color: oklch(0.561 0.129 256.8);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3f75bf;
  --color-fading-night-50: #dff7ff;
  --color-fading-night-100: #ceeaff;
  --color-fading-night-200: #b3d6ff;
  --color-fading-night-300: #8fb9f9;
  --color-fading-night-400: #6ba0ea;
  --color-fading-night-500: #4a86da;
  --color-fading-night-600: #3f72b8;
  --color-fading-night-700: #325b94;
  --color-fading-night-800: #20436e;
  --color-fading-night-900: #152e4d;
  --color-fading-night-950: #071b33;
}

SCSS

$fading-night: #3f75bf;
$fading-night-rgb: 63, 117, 191;
$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);
}