#3475D2

CSS

:root {
  --fading-night: #3475d2;
  --fading-night-rgb: 52 117 210;
  --fading-night-oklch: oklch(0.569 0.158 257.9);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 64% 51%);
  border-color: oklch(0.569 0.158 257.9);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3475d2;
  --color-fading-night-50: #dbf7ff;
  --color-fading-night-100: #c9eaff;
  --color-fading-night-200: #add6ff;
  --color-fading-night-300: #87b8ff;
  --color-fading-night-400: #609ffa;
  --color-fading-night-500: #3a84ec;
  --color-fading-night-600: #3370c7;
  --color-fading-night-700: #2859a0;
  --color-fading-night-800: #174277;
  --color-fading-night-900: #0f2e54;
  --color-fading-night-950: #031a39;
}

SCSS

$fading-night: #3475d2;
$fading-night-rgb: 52, 117, 210;
$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);
}