#324F5F

CSS

:root {
  --shadow-of-night: #324f5f;
  --shadow-of-night-rgb: 50 79 95;
  --shadow-of-night-oklch: oklch(0.412 0.044 233.5);
}

.element {
  color: var(--shadow-of-night);
  background-color: hsl(201 31% 28%);
  border-color: oklch(0.412 0.044 233.5);
}

Tailwind CSS v4

@theme {
  --color-shadow-of-night: #324f5f;
  --color-shadow-of-night-50: #eaf7ff;
  --color-shadow-of-night-100: #dbebf5;
  --color-shadow-of-night-200: #c3d8e5;
  --color-shadow-of-night-300: #a3bccb;
  --color-shadow-of-night-400: #85a3b5;
  --color-shadow-of-night-500: #698c9f;
  --color-shadow-of-night-600: #5a7686;
  --color-shadow-of-night-700: #475e6c;
  --color-shadow-of-night-800: #33454f;
  --color-shadow-of-night-900: #233037;
  --color-shadow-of-night-950: #121c22;
}

SCSS

$shadow-of-night: #324f5f;
$shadow-of-night-rgb: 50, 79, 95;
$shadow-of-night-light: mix(#fff, $shadow-of-night, 20%);
$shadow-of-night-dark: mix(#000, $shadow-of-night, 20%);

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