#3A78C4

CSS

:root {
  --fading-night: #3a78c4;
  --fading-night-rgb: 58 120 196;
  --fading-night-oklch: oklch(0.569 0.134 255);
}

.element {
  color: var(--fading-night);
  background-color: hsl(213 54% 50%);
  border-color: oklch(0.569 0.134 255);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #3a78c4;
  --color-fading-night-50: #ddf7ff;
  --color-fading-night-100: #cceaff;
  --color-fading-night-200: #b0d7ff;
  --color-fading-night-300: #8bbafc;
  --color-fading-night-400: #65a1ec;
  --color-fading-night-500: #4187dd;
  --color-fading-night-600: #3873ba;
  --color-fading-night-700: #2d5c96;
  --color-fading-night-800: #1c446f;
  --color-fading-night-900: #122f4e;
  --color-fading-night-950: #041b34;
}

SCSS

$fading-night: #3a78c4;
$fading-night-rgb: 58, 120, 196;
$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);
}