#3674CC

CSS

:root {
  --fading-night: #3674cc;
  --fading-night-rgb: 54 116 204;
  --fading-night-oklch: oklch(0.564 0.151 257.7);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 60% 51%);
  border-color: oklch(0.564 0.151 257.7);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3674cc;
  --color-fading-night-50: #dcf7ff;
  --color-fading-night-100: #cbeaff;
  --color-fading-night-200: #aed6ff;
  --color-fading-night-300: #89b8ff;
  --color-fading-night-400: #639ff6;
  --color-fading-night-500: #3f84e8;
  --color-fading-night-600: #3670c3;
  --color-fading-night-700: #2b5a9d;
  --color-fading-night-800: #1a4275;
  --color-fading-night-900: #112e53;
  --color-fading-night-950: #041a37;
}

SCSS

$fading-night: #3674cc;
$fading-night-rgb: 54, 116, 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);
}