#297399

CSS

:root {
  --harbour-blue: #297399;
  --harbour-blue-rgb: 41 115 153;
  --harbour-blue-oklch: oklch(0.527 0.093 235.1);
}

.element {
  color: var(--harbour-blue);
  background-color: hsl(200 58% 38%);
  border-color: oklch(0.527 0.093 235.1);
}

Tailwind CSS v4

@theme {
  --color-harbour-blue: #297399;
  --color-harbour-blue-50: #ddfaff;
  --color-harbour-blue-100: #ccedff;
  --color-harbour-blue-200: #afdbf8;
  --color-harbour-blue-300: #89bfe1;
  --color-harbour-blue-400: #64a7ce;
  --color-harbour-blue-500: #3e90bb;
  --color-harbour-blue-600: #36799e;
  --color-harbour-blue-700: #2b617f;
  --color-harbour-blue-800: #1c485d;
  --color-harbour-blue-900: #123241;
  --color-harbour-blue-950: #041d2a;
}

SCSS

$harbour-blue: #297399;
$harbour-blue-rgb: 41, 115, 153;
$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);
}