#4075C1

CSS

:root {
  --fading-night: #4075c1;
  --fading-night-rgb: 64 117 193;
  --fading-night-oklch: oklch(0.563 0.131 257.6);
}

.element {
  color: var(--fading-night);
  background-color: hsl(215 51% 50%);
  border-color: oklch(0.563 0.131 257.6);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #4075c1;
  --color-fading-night-50: #dff7ff;
  --color-fading-night-100: #ceeaff;
  --color-fading-night-200: #b3d6ff;
  --color-fading-night-300: #8fb9fb;
  --color-fading-night-400: #6ca0eb;
  --color-fading-night-500: #4a86db;
  --color-fading-night-600: #4071b9;
  --color-fading-night-700: #325b95;
  --color-fading-night-800: #21436f;
  --color-fading-night-900: #162e4e;
  --color-fading-night-950: #071b34;
}

SCSS

$fading-night: #4075c1;
$fading-night-rgb: 64, 117, 193;
$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);
}