#4377C3

CSS

:root {
  --fading-night: #4377c3;
  --fading-night-rgb: 67 119 195;
  --fading-night-oklch: oklch(0.57 0.131 257.9);
}

.element {
  color: var(--fading-night);
  background-color: hsl(216 52% 51%);
  border-color: oklch(0.57 0.131 257.9);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #4377c3;
  --color-fading-night-50: #e0f7ff;
  --color-fading-night-100: #cfe9ff;
  --color-fading-night-200: #b4d6ff;
  --color-fading-night-300: #90b8fa;
  --color-fading-night-400: #6ca0eb;
  --color-fading-night-500: #4b86db;
  --color-fading-night-600: #4071b9;
  --color-fading-night-700: #335b95;
  --color-fading-night-800: #21436f;
  --color-fading-night-900: #162e4e;
  --color-fading-night-950: #071b34;
}

SCSS

$fading-night: #4377c3;
$fading-night-rgb: 67, 119, 195;
$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);
}