#00404B

CSS

:root {
  --cold-and-dark: #00404b;
  --cold-and-dark-rgb: 0 64 75;
  --cold-and-dark-oklch: oklch(0.341 0.06 213.6);
}

.element {
  color: var(--cold-and-dark);
  background-color: hsl(189 100% 15%);
  border-color: oklch(0.341 0.06 213.6);
}

Tailwind CSS v4

@theme {
  --color-cold-and-dark: #00404b;
  --color-cold-and-dark-50: #e3faff;
  --color-cold-and-dark-100: #d2edf5;
  --color-cold-and-dark-200: #b8dbe5;
  --color-cold-and-dark-300: #95c0cb;
  --color-cold-and-dark-400: #75a8b4;
  --color-cold-and-dark-500: #54919e;
  --color-cold-and-dark-600: #487a86;
  --color-cold-and-dark-700: #39626b;
  --color-cold-and-dark-800: #28484e;
  --color-cold-and-dark-900: #1b3236;
  --color-cold-and-dark-950: #0b1e21;
}

SCSS

$cold-and-dark: #00404b;
$cold-and-dark-rgb: 0, 64, 75;
$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);
}