#4573C4

CSS

:root {
  --fading-night: #4573c4;
  --fading-night-rgb: 69 115 196;
  --fading-night-oklch: oklch(0.563 0.136 260.9);
}

.element {
  color: var(--fading-night);
  background-color: hsl(218 52% 52%);
  border-color: oklch(0.563 0.136 260.9);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #4573c4;
  --color-fading-night-50: #e1f6ff;
  --color-fading-night-100: #d0e9ff;
  --color-fading-night-200: #b6d5ff;
  --color-fading-night-300: #92b7fd;
  --color-fading-night-400: #709eee;
  --color-fading-night-500: #5084df;
  --color-fading-night-600: #4470bc;
  --color-fading-night-700: #365997;
  --color-fading-night-800: #244271;
  --color-fading-night-900: #182d4f;
  --color-fading-night-950: #091a35;
}

SCSS

$fading-night: #4573c4;
$fading-night-rgb: 69, 115, 196;
$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);
}