#667799

CSS

:root {
  --misty-harbour: #667799;
  --misty-harbour-rgb: 102 119 153;
  --misty-harbour-oklch: oklch(0.569 0.057 264);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(220 20% 50%);
  border-color: oklch(0.569 0.057 264);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #667799;
  --color-misty-harbour-50: #edf5ff;
  --color-misty-harbour-100: #dfe8fc;
  --color-misty-harbour-200: #c9d4ed;
  --color-misty-harbour-300: #aab7d5;
  --color-misty-harbour-400: #8e9fc1;
  --color-misty-harbour-500: #7386ac;
  --color-misty-harbour-600: #627292;
  --color-misty-harbour-700: #4e5b75;
  --color-misty-harbour-800: #384356;
  --color-misty-harbour-900: #262e3c;
  --color-misty-harbour-950: #141b26;
}

SCSS

$misty-harbour: #667799;
$misty-harbour-rgb: 102, 119, 153;
$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);
}