#3D75C2

CSS

:root {
  --fading-night: #3d75c2;
  --fading-night-rgb: 61 117 194;
  --fading-night-oklch: oklch(0.562 0.134 256.9);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 52% 50%);
  border-color: oklch(0.562 0.134 256.9);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3d75c2;
  --color-fading-night-50: #dff7ff;
  --color-fading-night-100: #cdeaff;
  --color-fading-night-200: #b2d6ff;
  --color-fading-night-300: #8eb9fc;
  --color-fading-night-400: #69a0ec;
  --color-fading-night-500: #4786dd;
  --color-fading-night-600: #3d72ba;
  --color-fading-night-700: #305b96;
  --color-fading-night-800: #1f436f;
  --color-fading-night-900: #142e4e;
  --color-fading-night-950: #061b34;
}

SCSS

$fading-night: #3d75c2;
$fading-night-rgb: 61, 117, 194;
$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);
}