#637599

CSS

:root {
  --misty-harbour: #637599;
  --misty-harbour-rgb: 99 117 153;
  --misty-harbour-oklch: oklch(0.562 0.06 263.9);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(220 21% 49%);
  border-color: oklch(0.562 0.06 263.9);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #637599;
  --color-misty-harbour-50: #edf5ff;
  --color-misty-harbour-100: #dee8fd;
  --color-misty-harbour-200: #c8d4ef;
  --color-misty-harbour-300: #a9b7d7;
  --color-misty-harbour-400: #8c9fc3;
  --color-misty-harbour-500: #7286af;
  --color-misty-harbour-600: #617294;
  --color-misty-harbour-700: #4d5b76;
  --color-misty-harbour-800: #374358;
  --color-misty-harbour-900: #262e3d;
  --color-misty-harbour-950: #141b27;
}

SCSS

$misty-harbour: #637599;
$misty-harbour-rgb: 99, 117, 153;
$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);
}