#213743

CSS

:root {
  --into-the-night: #213743;
  --into-the-night-rgb: 33 55 67;
  --into-the-night-oklch: oklch(0.324 0.035 233.2);
}

.element {
  color: var(--into-the-night);
  background-color: hsl(201 34% 20%);
  border-color: oklch(0.324 0.035 233.2);
}

Tailwind CSS v4

@theme {
  --color-into-the-night: #213743;
  --color-into-the-night-50: #ecf7fe;
  --color-into-the-night-100: #ddeaf2;
  --color-into-the-night-200: #c7d7e1;
  --color-into-the-night-300: #a7bbc7;
  --color-into-the-night-400: #8ba2b0;
  --color-into-the-night-500: #708b9a;
  --color-into-the-night-600: #5f7582;
  --color-into-the-night-700: #4c5e68;
  --color-into-the-night-800: #36454c;
  --color-into-the-night-900: #253035;
  --color-into-the-night-950: #141c20;
}

SCSS

$into-the-night: #213743;
$into-the-night-rgb: 33, 55, 67;
$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);
}