#2872DA

CSS

:root {
  --fading-night: #2872da;
  --fading-night-rgb: 40 114 218;
  --fading-night-oklch: oklch(0.564 0.175 258);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 71% 51%);
  border-color: oklch(0.564 0.175 258);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #2872da;
  --color-fading-night-50: #d8f7ff;
  --color-fading-night-100: #c6eaff;
  --color-fading-night-200: #a8d6ff;
  --color-fading-night-300: #81b7ff;
  --color-fading-night-400: #589eff;
  --color-fading-night-500: #2f82f7;
  --color-fading-night-600: #296ed0;
  --color-fading-night-700: #2158a7;
  --color-fading-night-800: #10417d;
  --color-fading-night-900: #0a2d58;
  --color-fading-night-950: #00193c;
}

SCSS

$fading-night: #2872da;
$fading-night-rgb: 40, 114, 218;
$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);
}