#2377D1

CSS

:root {
  --fading-night: #2377d1;
  --fading-night-rgb: 35 119 209;
  --fading-night-oklch: oklch(0.568 0.159 253.9);
}

.element {
  color: var(--fading-night);
  background-color: hsl(211 71% 48%);
  border-color: oklch(0.568 0.159 253.9);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #2377d1;
  --color-fading-night-50: #d8f8ff;
  --color-fading-night-100: #c5ebff;
  --color-fading-night-200: #a7d7ff;
  --color-fading-night-300: #80baff;
  --color-fading-night-400: #55a1f9;
  --color-fading-night-500: #2786ec;
  --color-fading-night-600: #2472c7;
  --color-fading-night-700: #1d5ba0;
  --color-fading-night-800: #0c4377;
  --color-fading-night-900: #082f54;
  --color-fading-night-950: #001b38;
}

SCSS

$fading-night: #2377d1;
$fading-night-rgb: 35, 119, 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);
}