#3976CC

CSS

:root {
  --fading-night: #3976cc;
  --fading-night-rgb: 57 118 204;
  --fading-night-oklch: oklch(0.569 0.147 257.5);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 59% 51%);
  border-color: oklch(0.569 0.147 257.5);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3976cc;
  --color-fading-night-50: #ddf7ff;
  --color-fading-night-100: #cbeaff;
  --color-fading-night-200: #afd6ff;
  --color-fading-night-300: #8ab8ff;
  --color-fading-night-400: #649ff4;
  --color-fading-night-500: #4085e6;
  --color-fading-night-600: #3771c2;
  --color-fading-night-700: #2c5a9c;
  --color-fading-night-800: #1b4274;
  --color-fading-night-900: #112e52;
  --color-fading-night-950: #041a37;
}

SCSS

$fading-night: #3976cc;
$fading-night-rgb: 57, 118, 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);
}