#4577C1

CSS

:root {
  --fading-night: #4577c1;
  --fading-night-rgb: 69 119 193;
  --fading-night-oklch: oklch(0.57 0.127 258.1);
}

.element {
  color: var(--fading-night);
  background-color: hsl(216 50% 51%);
  border-color: oklch(0.57 0.127 258.1);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #4577c1;
  --color-fading-night-50: #e0f7ff;
  --color-fading-night-100: #d0e9ff;
  --color-fading-night-200: #b5d6ff;
  --color-fading-night-300: #91b8f9;
  --color-fading-night-400: #6ea0e9;
  --color-fading-night-500: #4e86d9;
  --color-fading-night-600: #4271b7;
  --color-fading-night-700: #355b93;
  --color-fading-night-800: #23436d;
  --color-fading-night-900: #172e4d;
  --color-fading-night-950: #081b33;
}

SCSS

$fading-night: #4577c1;
$fading-night-rgb: 69, 119, 193;
$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);
}