#4073CB

CSS

:root {
  --fading-night: #4073cb;
  --fading-night-rgb: 64 115 203;
  --fading-night-oklch: oklch(0.565 0.147 260.5);
}

.element {
  color: var(--fading-night);
  background-color: hsl(218 57% 52%);
  border-color: oklch(0.565 0.147 260.5);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #4073cb;
  --color-fading-night-50: #dff6ff;
  --color-fading-night-100: #cee9ff;
  --color-fading-night-200: #b3d5ff;
  --color-fading-night-300: #8fb7ff;
  --color-fading-night-400: #6b9ef5;
  --color-fading-night-500: #4983e6;
  --color-fading-night-600: #3f6fc2;
  --color-fading-night-700: #32599c;
  --color-fading-night-800: #204174;
  --color-fading-night-900: #152d52;
  --color-fading-night-950: #071a37;
}

SCSS

$fading-night: #4073cb;
$fading-night-rgb: 64, 115, 203;
$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);
}