#19204B

CSS

:root {
  --fly-by-night: #19204b;
  --fly-by-night-rgb: 25 32 75;
  --fly-by-night-oklch: oklch(0.264 0.08 272.8);
}

.element {
  color: var(--fly-by-night);
  background-color: hsl(232 50% 20%);
  border-color: oklch(0.264 0.08 272.8);
}

Tailwind CSS v4

@theme {
  --color-fly-by-night: #19204b;
  --color-fly-by-night-50: #eef4ff;
  --color-fly-by-night-100: #e0e6ff;
  --color-fly-by-night-200: #cad2f7;
  --color-fly-by-night-300: #abb5e1;
  --color-fly-by-night-400: #8e9cce;
  --color-fly-by-night-500: #7483bb;
  --color-fly-by-night-600: #636f9e;
  --color-fly-by-night-700: #4f587f;
  --color-fly-by-night-800: #38415e;
  --color-fly-by-night-900: #262d42;
  --color-fly-by-night-950: #151a2a;
}

SCSS

$fly-by-night: #19204b;
$fly-by-night-rgb: 25, 32, 75;
$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);
}