#4374C5

CSS

:root {
  --fading-night: #4374c5;
  --fading-night-rgb: 67 116 197;
  --fading-night-oklch: oklch(0.565 0.137 259.9);
}

.element {
  color: var(--fading-night);
  background-color: hsl(217 53% 52%);
  border-color: oklch(0.565 0.137 259.9);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #4374c5;
  --color-fading-night-50: #e0f6ff;
  --color-fading-night-100: #cfe9ff;
  --color-fading-night-200: #b4d5ff;
  --color-fading-night-300: #91b8fe;
  --color-fading-night-400: #6d9eef;
  --color-fading-night-500: #4d84df;
  --color-fading-night-600: #4270bc;
  --color-fading-night-700: #345a97;
  --color-fading-night-800: #224271;
  --color-fading-night-900: #162e50;
  --color-fading-night-950: #081a35;
}

SCSS

$fading-night: #4374c5;
$fading-night-rgb: 67, 116, 197;
$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);
}