#004559

CSS

:root {
  --cold-and-dark: #004559;
  --cold-and-dark-rgb: 0 69 89;
  --cold-and-dark-oklch: oklch(0.363 0.069 225);
}

.element {
  color: var(--cold-and-dark);
  background-color: hsl(193 100% 17%);
  border-color: oklch(0.363 0.069 225);
}

Tailwind CSS v4

@theme {
  --color-cold-and-dark: #004559;
  --color-cold-and-dark-50: #e2faff;
  --color-cold-and-dark-100: #d1edfa;
  --color-cold-and-dark-200: #b6dbeb;
  --color-cold-and-dark-300: #93bfd3;
  --color-cold-and-dark-400: #71a8bd;
  --color-cold-and-dark-500: #5090a9;
  --color-cold-and-dark-600: #447a8e;
  --color-cold-and-dark-700: #366172;
  --color-cold-and-dark-800: #264854;
  --color-cold-and-dark-900: #19323a;
  --color-cold-and-dark-950: #091e24;
}

SCSS

$cold-and-dark: #004559;
$cold-and-dark-rgb: 0, 69, 89;
$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);
}