#657794

CSS

:root {
  --misty-harbour: #657794;
  --misty-harbour-rgb: 101 119 148;
  --misty-harbour-oklch: oklch(0.566 0.05 259.9);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(217 19% 49%);
  border-color: oklch(0.566 0.05 259.9);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #657794;
  --color-misty-harbour-50: #edf6ff;
  --color-misty-harbour-100: #dfe8f9;
  --color-misty-harbour-200: #c9d5ea;
  --color-misty-harbour-300: #aab8d2;
  --color-misty-harbour-400: #8d9fbd;
  --color-misty-harbour-500: #7387a8;
  --color-misty-harbour-600: #61728e;
  --color-misty-harbour-700: #4e5b72;
  --color-misty-harbour-800: #384354;
  --color-misty-harbour-900: #262e3a;
  --color-misty-harbour-950: #141b25;
}

SCSS

$misty-harbour: #657794;
$misty-harbour-rgb: 101, 119, 148;
$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);
}