#3576D1

CSS

:root {
  --fading-night: #3576d1;
  --fading-night-rgb: 53 118 209;
  --fading-night-oklch: oklch(0.571 0.155 257.5);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 63% 51%);
  border-color: oklch(0.571 0.155 257.5);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3576d1;
  --color-fading-night-50: #dbf7ff;
  --color-fading-night-100: #caeaff;
  --color-fading-night-200: #add6ff;
  --color-fading-night-300: #87b8ff;
  --color-fading-night-400: #609ff9;
  --color-fading-night-500: #3b84ea;
  --color-fading-night-600: #3370c6;
  --color-fading-night-700: #295a9f;
  --color-fading-night-800: #184277;
  --color-fading-night-900: #0f2e54;
  --color-fading-night-950: #031a38;
}

SCSS

$fading-night: #3576d1;
$fading-night-rgb: 53, 118, 209;
$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);
}