#1575D4

CSS

:root {
  --fading-night: #1575d4;
  --fading-night-rgb: 21 117 212;
  --fading-night-oklch: oklch(0.563 0.168 253.7);
}

.element {
  color: var(--fading-night);
  background-color: hsl(210 82% 46%);
  border-color: oklch(0.563 0.168 253.7);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #1575d4;
  --color-fading-night-50: #d6f8ff;
  --color-fading-night-100: #c3ebff;
  --color-fading-night-200: #a4d7ff;
  --color-fading-night-300: #7cbaff;
  --color-fading-night-400: #4fa1fe;
  --color-fading-night-500: #1a86f1;
  --color-fading-night-600: #1a72cb;
  --color-fading-night-700: #155ba3;
  --color-fading-night-800: #05437a;
  --color-fading-night-900: #042e56;
  --color-fading-night-950: #001b3a;
}

SCSS

$fading-night: #1575d4;
$fading-night-rgb: 21, 117, 212;
$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);
}