#1375D3

CSS

:root {
  --fading-night: #1375d3;
  --fading-night-rgb: 19 117 211;
  --fading-night-oklch: oklch(0.562 0.167 253.3);
}

.element {
  color: var(--fading-night);
  background-color: hsl(209 83% 45%);
  border-color: oklch(0.562 0.167 253.3);
}

Tailwind CSS v4

@theme {
  --color-fading-night: #1375d3;
  --color-fading-night-50: #d6f8ff;
  --color-fading-night-100: #c3ebff;
  --color-fading-night-200: #a4d8ff;
  --color-fading-night-300: #7bbaff;
  --color-fading-night-400: #4fa1fe;
  --color-fading-night-500: #1886f0;
  --color-fading-night-600: #1972ca;
  --color-fading-night-700: #145ba3;
  --color-fading-night-800: #044379;
  --color-fading-night-900: #042f56;
  --color-fading-night-950: #001b3a;
}

SCSS

$fading-night: #1375d3;
$fading-night-rgb: 19, 117, 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);
}