#6373A3

CSS

:root {
  --misty-harbour: #6373a3;
  --misty-harbour-rgb: 99 115 163;
  --misty-harbour-oklch: oklch(0.562 0.077 269.7);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(225 26% 51%);
  border-color: oklch(0.562 0.077 269.7);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #6373a3;
  --color-misty-harbour-50: #edf4ff;
  --color-misty-harbour-100: #dee7ff;
  --color-misty-harbour-200: #c8d3f6;
  --color-misty-harbour-300: #a9b6e0;
  --color-misty-harbour-400: #8c9dcd;
  --color-misty-harbour-500: #7284ba;
  --color-misty-harbour-600: #60709d;
  --color-misty-harbour-700: #4d597e;
  --color-misty-harbour-800: #37415d;
  --color-misty-harbour-900: #252d41;
  --color-misty-harbour-950: #141a2a;
}

SCSS

$misty-harbour: #6373a3;
$misty-harbour-rgb: 99, 115, 163;
$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);
}