#003946

CSS

:root {
  --cold-and-dark: #003946;
  --cold-and-dark-rgb: 0 57 70;
  --cold-and-dark-oklch: oklch(0.318 0.057 218.7);
}

.element {
  color: var(--cold-and-dark);
  background-color: hsl(191 100% 14%);
  border-color: oklch(0.318 0.057 218.7);
}

Tailwind CSS v4

@theme {
  --color-cold-and-dark: #003946;
  --color-cold-and-dark-50: #e4f9ff;
  --color-cold-and-dark-100: #d4edf5;
  --color-cold-and-dark-200: #badbe6;
  --color-cold-and-dark-300: #98bfcc;
  --color-cold-and-dark-400: #78a7b5;
  --color-cold-and-dark-500: #5890a0;
  --color-cold-and-dark-600: #4b7a87;
  --color-cold-and-dark-700: #3c616c;
  --color-cold-and-dark-800: #2a474f;
  --color-cold-and-dark-900: #1c3237;
  --color-cold-and-dark-950: #0c1d22;
}

SCSS

$cold-and-dark: #003946;
$cold-and-dark-rgb: 0, 57, 70;
$cold-and-dark-light: mix(#fff, $cold-and-dark, 20%);
$cold-and-dark-dark: mix(#000, $cold-and-dark, 20%);

.element {
  color: $cold-and-dark;
  box-shadow: 0 0 0 2px rgba($cold-and-dark, 0.35);
}