#687399

CSS

:root {
  --misty-harbour: #687399;
  --misty-harbour-rgb: 104 115 153;
  --misty-harbour-oklch: oklch(0.561 0.061 271.8);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(227 19% 50%);
  border-color: oklch(0.561 0.061 271.8);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #687399;
  --color-misty-harbour-50: #eff4ff;
  --color-misty-harbour-100: #e1e7fd;
  --color-misty-harbour-200: #ccd3ef;
  --color-misty-harbour-300: #adb6d7;
  --color-misty-harbour-400: #919dc3;
  --color-misty-harbour-500: #7884af;
  --color-misty-harbour-600: #657094;
  --color-misty-harbour-700: #515977;
  --color-misty-harbour-800: #3a4258;
  --color-misty-harbour-900: #282d3d;
  --color-misty-harbour-950: #161a27;
}

SCSS

$misty-harbour: #687399;
$misty-harbour-rgb: 104, 115, 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);
}