#2178CF

CSS

:root {
  --fading-night: #2178cf;
  --fading-night-rgb: 33 120 207;
  --fading-night-oklch: oklch(0.569 0.156 252.7);
}

.element {
  color: var(--fading-night);
  background-color: hsl(210 73% 47%);
  border-color: oklch(0.569 0.156 252.7);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #2178cf;
  --color-fading-night-50: #d8f8ff;
  --color-fading-night-100: #c5ebff;
  --color-fading-night-200: #a7d8ff;
  --color-fading-night-300: #7fbbff;
  --color-fading-night-400: #54a2f7;
  --color-fading-night-500: #2587e9;
  --color-fading-night-600: #2273c5;
  --color-fading-night-700: #1b5c9e;
  --color-fading-night-800: #0b4476;
  --color-fading-night-900: #072f53;
  --color-fading-night-950: #001b38;
}

SCSS

$fading-night: #2178cf;
$fading-night-rgb: 33, 120, 207;
$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);
}