#647798

CSS

:root {
  --misty-harbour: #647798;
  --misty-harbour-rgb: 100 119 152;
  --misty-harbour-oklch: oklch(0.567 0.056 261.3);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(218 21% 49%);
  border-color: oklch(0.567 0.056 261.3);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #647798;
  --color-misty-harbour-50: #edf6ff;
  --color-misty-harbour-100: #dee8fb;
  --color-misty-harbour-200: #c8d5ed;
  --color-misty-harbour-300: #a9b8d5;
  --color-misty-harbour-400: #8c9fc0;
  --color-misty-harbour-500: #7187ac;
  --color-misty-harbour-600: #607291;
  --color-misty-harbour-700: #4d5b74;
  --color-misty-harbour-800: #374356;
  --color-misty-harbour-900: #252e3c;
  --color-misty-harbour-950: #141b26;
}

SCSS

$misty-harbour: #647798;
$misty-harbour-rgb: 100, 119, 152;
$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);
}