#003D4E

CSS

:root {
  --cold-and-dark: #003d4e;
  --cold-and-dark-rgb: 0 61 78;
  --cold-and-dark-oklch: oklch(0.334 0.063 223.5);
}

.element {
  color: var(--cold-and-dark);
  background-color: hsl(193 100% 15%);
  border-color: oklch(0.334 0.063 223.5);
}

Tailwind CSS v4

@theme {
  --color-cold-and-dark: #003d4e;
  --color-cold-and-dark-50: #e3f9ff;
  --color-cold-and-dark-100: #d3edf8;
  --color-cold-and-dark-200: #b9dae9;
  --color-cold-and-dark-300: #96bfd0;
  --color-cold-and-dark-400: #75a7ba;
  --color-cold-and-dark-500: #558fa5;
  --color-cold-and-dark-600: #49798b;
  --color-cold-and-dark-700: #3a6170;
  --color-cold-and-dark-800: #294752;
  --color-cold-and-dark-900: #1b3139;
  --color-cold-and-dark-950: #0b1d23;
}

SCSS

$cold-and-dark: #003d4e;
$cold-and-dark-rgb: 0, 61, 78;
$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);
}