#1C1D4A

CSS

:root {
  --fly-by-night: #1c1d4a;
  --fly-by-night-rgb: 28 29 74;
  --fly-by-night-oklch: oklch(0.259 0.082 278.1);
}

.element {
  color: var(--fly-by-night);
  background-color: hsl(239 45% 20%);
  border-color: oklch(0.259 0.082 278.1);
}

Tailwind CSS v4

@theme {
  --color-fly-by-night: #1c1d4a;
  --color-fly-by-night-50: #f0f3ff;
  --color-fly-by-night-100: #e2e6ff;
  --color-fly-by-night-200: #cdd1f7;
  --color-fly-by-night-300: #afb3e1;
  --color-fly-by-night-400: #939acf;
  --color-fly-by-night-500: #7981bc;
  --color-fly-by-night-600: #676d9f;
  --color-fly-by-night-700: #52577f;
  --color-fly-by-night-800: #3b405f;
  --color-fly-by-night-900: #282c42;
  --color-fly-by-night-950: #16192b;
}

SCSS

$fly-by-night: #1c1d4a;
$fly-by-night-rgb: 28, 29, 74;
$fly-by-night-light: mix(#fff, $fly-by-night, 20%);
$fly-by-night-dark: mix(#000, $fly-by-night, 20%);

.element {
  color: $fly-by-night;
  box-shadow: 0 0 0 2px rgba($fly-by-night, 0.35);
}