#66758F

CSS

:root {
  --misty-harbour: #66758f;
  --misty-harbour-rgb: 102 117 143;
  --misty-harbour-oklch: oklch(0.56 0.044 261.4);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(218 17% 48%);
  border-color: oklch(0.56 0.044 261.4);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #66758f;
  --color-misty-harbour-50: #eff5ff;
  --color-misty-harbour-100: #e0e8f7;
  --color-misty-harbour-200: #cad5e8;
  --color-misty-harbour-300: #acb8cf;
  --color-misty-harbour-400: #909fb9;
  --color-misty-harbour-500: #7687a4;
  --color-misty-harbour-600: #64728b;
  --color-misty-harbour-700: #505b6f;
  --color-misty-harbour-800: #394352;
  --color-misty-harbour-900: #272e39;
  --color-misty-harbour-950: #151b23;
}

SCSS

$misty-harbour: #66758f;
$misty-harbour-rgb: 102, 117, 143;
$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);
}