#347AD3

CSS

:root {
  --fading-night: #347ad3;
  --fading-night-rgb: 52 122 211;
  --fading-night-oklch: oklch(0.581 0.154 256);
}

.element {
  color: var(--fading-night);
  background-color: hsl(214 64% 52%);
  border-color: oklch(0.581 0.154 256);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #347ad3;
  --color-fading-night-50: #daf7ff;
  --color-fading-night-100: #c9eaff;
  --color-fading-night-200: #abd7ff;
  --color-fading-night-300: #85b9ff;
  --color-fading-night-400: #5da0f7;
  --color-fading-night-500: #3685e9;
  --color-fading-night-600: #2f71c4;
  --color-fading-night-700: #265a9e;
  --color-fading-night-800: #154376;
  --color-fading-night-900: #0e2e53;
  --color-fading-night-950: #021a38;
}

SCSS

$fading-night: #347ad3;
$fading-night-rgb: 52, 122, 211;
$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);
}