#3F728D

CSS

:root {
  --harbour-blue: #3f728d;
  --harbour-blue-rgb: 63 114 141;
  --harbour-blue-oklch: oklch(0.528 0.069 233.3);
}

.element {
  color: var(--harbour-blue);
  background-color: hsl(201 38% 40%);
  border-color: oklch(0.528 0.069 233.3);
}

Tailwind CSS v4

@theme {
  --color-harbour-blue: #3f728d;
  --color-harbour-blue-50: #e3f9ff;
  --color-harbour-blue-100: #d3ecfc;
  --color-harbour-blue-200: #b9daee;
  --color-harbour-blue-300: #96bed6;
  --color-harbour-blue-400: #75a6c1;
  --color-harbour-blue-500: #558ead;
  --color-harbour-blue-600: #487892;
  --color-harbour-blue-700: #3a6075;
  --color-harbour-blue-800: #284756;
  --color-harbour-blue-900: #1b313c;
  --color-harbour-blue-950: #0b1d26;
}

SCSS

$harbour-blue: #3f728d;
$harbour-blue-rgb: 63, 114, 141;
$harbour-blue-light: mix(#fff, $harbour-blue, 20%);
$harbour-blue-dark: mix(#000, $harbour-blue, 20%);

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