#2574D3

CSS

:root {
  --fading-night: #2574d3;
  --fading-night-rgb: 37 116 211;
  --fading-night-oklch: oklch(0.563 0.164 255.7);
}

.element {
  color: var(--fading-night);
  background-color: hsl(213 70% 49%);
  border-color: oklch(0.563 0.164 255.7);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #2574d3;
  --color-fading-night-50: #d8f8ff;
  --color-fading-night-100: #c6eaff;
  --color-fading-night-200: #a8d7ff;
  --color-fading-night-300: #81b9ff;
  --color-fading-night-400: #57a0fd;
  --color-fading-night-500: #2c85f0;
  --color-fading-night-600: #2771ca;
  --color-fading-night-700: #1f5aa2;
  --color-fading-night-800: #0f4279;
  --color-fading-night-900: #092e56;
  --color-fading-night-950: #001a3a;
}

SCSS

$fading-night: #2574d3;
$fading-night-rgb: 37, 116, 211;
$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);
}