#2578CC

CSS

:root {
  --fading-night: #2578cc;
  --fading-night-rgb: 37 120 204;
  --fading-night-oklch: oklch(0.568 0.151 252.6);
}

.element {
  color: var(--fading-night);
  background-color: hsl(210 69% 47%);
  border-color: oklch(0.568 0.151 252.6);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #2578cc;
  --color-fading-night-50: #d8f8ff;
  --color-fading-night-100: #c6ebff;
  --color-fading-night-200: #a8d8ff;
  --color-fading-night-300: #81bbff;
  --color-fading-night-400: #57a2f5;
  --color-fading-night-500: #2a88e6;
  --color-fading-night-600: #2673c2;
  --color-fading-night-700: #1e5c9c;
  --color-fading-night-800: #0e4474;
  --color-fading-night-900: #092f52;
  --color-fading-night-950: #001b37;
}

SCSS

$fading-night: #2578cc;
$fading-night-rgb: 37, 120, 204;
$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);
}