#18313D

CSS

:root {
  --into-the-night: #18313d;
  --into-the-night-rgb: 24 49 61;
  --into-the-night-oklch: oklch(0.299 0.038 230.7);
}

.element {
  color: var(--into-the-night);
  background-color: hsl(199 44% 17%);
  border-color: oklch(0.299 0.038 230.7);
}

Tailwind CSS v4

@theme {
  --color-into-the-night: #18313d;
  --color-into-the-night-50: #ebf7fe;
  --color-into-the-night-100: #dceaf3;
  --color-into-the-night-200: #c5d7e2;
  --color-into-the-night-300: #a5bbc8;
  --color-into-the-night-400: #88a3b1;
  --color-into-the-night-500: #6d8b9b;
  --color-into-the-night-600: #5c7683;
  --color-into-the-night-700: #4a5e69;
  --color-into-the-night-800: #35454d;
  --color-into-the-night-900: #243035;
  --color-into-the-night-950: #131c21;
}

SCSS

$into-the-night: #18313d;
$into-the-night-rgb: 24, 49, 61;
$into-the-night-light: mix(#fff, $into-the-night, 20%);
$into-the-night-dark: mix(#000, $into-the-night, 20%);

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