#64749A

CSS

:root {
  --misty-harbour: #64749a;
  --misty-harbour-rgb: 100 116 154;
  --misty-harbour-oklch: oklch(0.561 0.062 266.7);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(222 21% 50%);
  border-color: oklch(0.561 0.062 266.7);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #64749a;
  --color-misty-harbour-50: #eef5ff;
  --color-misty-harbour-100: #dfe8fe;
  --color-misty-harbour-200: #c9d4f0;
  --color-misty-harbour-300: #aab7d8;
  --color-misty-harbour-400: #8e9ec4;
  --color-misty-harbour-500: #7385b0;
  --color-misty-harbour-600: #627195;
  --color-misty-harbour-700: #4e5a77;
  --color-misty-harbour-800: #384258;
  --color-misty-harbour-900: #262e3e;
  --color-misty-harbour-950: #141a27;
}

SCSS

$misty-harbour: #64749a;
$misty-harbour-rgb: 100, 116, 154;
$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);
}