#2678CE

CSS

:root {
  --fading-night: #2678ce;
  --fading-night-rgb: 38 120 206;
  --fading-night-oklch: oklch(0.569 0.153 253.2);
}

.element {
  color: var(--fading-night);
  background-color: hsl(211 69% 48%);
  border-color: oklch(0.569 0.153 253.2);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #2678ce;
  --color-fading-night-50: #d8f8ff;
  --color-fading-night-100: #c6ebff;
  --color-fading-night-200: #a8d8ff;
  --color-fading-night-300: #81baff;
  --color-fading-night-400: #57a1f6;
  --color-fading-night-500: #2a87e8;
  --color-fading-night-600: #2673c3;
  --color-fading-night-700: #1e5c9d;
  --color-fading-night-800: #0f4475;
  --color-fading-night-900: #092f53;
  --color-fading-night-950: #001b37;
}

SCSS

$fading-night: #2678ce;
$fading-night-rgb: 38, 120, 206;
$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);
}