#66739D

CSS

:root {
  --misty-harbour: #66739d;
  --misty-harbour-rgb: 102 115 157;
  --misty-harbour-oklch: oklch(0.562 0.067 270.9);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(226 22% 51%);
  border-color: oklch(0.562 0.067 270.9);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #66739d;
  --color-misty-harbour-50: #eef4ff;
  --color-misty-harbour-100: #e0e7ff;
  --color-misty-harbour-200: #cad3f2;
  --color-misty-harbour-300: #acb6db;
  --color-misty-harbour-400: #8f9dc7;
  --color-misty-harbour-500: #7584b3;
  --color-misty-harbour-600: #637097;
  --color-misty-harbour-700: #4f597a;
  --color-misty-harbour-800: #39425a;
  --color-misty-harbour-900: #272d3f;
  --color-misty-harbour-950: #151a28;
}

SCSS

$misty-harbour: #66739d;
$misty-harbour-rgb: 102, 115, 157;
$misty-harbour-light: mix(#fff, $misty-harbour, 20%);
$misty-harbour-dark: mix(#000, $misty-harbour, 20%);

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