#2F73D4

CSS

:root {
  --fading-night: #2f73d4;
  --fading-night-rgb: 47 115 212;
  --fading-night-oklch: oklch(0.564 0.164 258);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 66% 51%);
  border-color: oklch(0.564 0.164 258);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #2f73d4;
  --color-fading-night-50: #daf7ff;
  --color-fading-night-100: #c8eaff;
  --color-fading-night-200: #abd6ff;
  --color-fading-night-300: #85b8ff;
  --color-fading-night-400: #5d9efe;
  --color-fading-night-500: #3683f0;
  --color-fading-night-600: #306fcb;
  --color-fading-night-700: #2659a3;
  --color-fading-night-800: #15427a;
  --color-fading-night-900: #0d2d56;
  --color-fading-night-950: #021a3a;
}

SCSS

$fading-night: #2f73d4;
$fading-night-rgb: 47, 115, 212;
$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);
}