#42728C

CSS

:root {
  --harbour-blue: #42728c;
  --harbour-blue-rgb: 66 114 140;
  --harbour-blue-oklch: oklch(0.529 0.066 233.6);
}

.element {
  color: var(--harbour-blue);
  background-color: hsl(201 36% 40%);
  border-color: oklch(0.529 0.066 233.6);
}

Tailwind CSS v4

@theme {
  --color-harbour-blue: #42728c;
  --color-harbour-blue-50: #e4f9ff;
  --color-harbour-blue-100: #d4ecfb;
  --color-harbour-blue-200: #bad9ed;
  --color-harbour-blue-300: #97bdd5;
  --color-harbour-blue-400: #77a6c0;
  --color-harbour-blue-500: #588eac;
  --color-harbour-blue-600: #4b7891;
  --color-harbour-blue-700: #3b6074;
  --color-harbour-blue-800: #294755;
  --color-harbour-blue-900: #1c313c;
  --color-harbour-blue-950: #0c1d25;
}

SCSS

$harbour-blue: #42728c;
$harbour-blue-rgb: 66, 114, 140;
$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);
}