#366AC3

CSS

:root {
  --matt-blue: #366ac3;
  --matt-blue-rgb: 54 106 195;
  --matt-blue-oklch: oklch(0.536 0.15 260.4);
}

.element {
  color: var(--matt-blue);
  background-color: hsl(218 57% 49%);
  border-color: oklch(0.536 0.15 260.4);
}

Tailwind CSS v4

@theme {
  --color-matt-blue: #366ac3;
  --color-matt-blue-50: #def6ff;
  --color-matt-blue-100: #cde9ff;
  --color-matt-blue-200: #b2d5ff;
  --color-matt-blue-300: #8eb7ff;
  --color-matt-blue-400: #699df6;
  --color-matt-blue-500: #4883e8;
  --color-matt-blue-600: #3d6fc4;
  --color-matt-blue-700: #31599d;
  --color-matt-blue-800: #1f4175;
  --color-matt-blue-900: #142d53;
  --color-matt-blue-950: #061a37;
}

SCSS

$matt-blue: #366ac3;
$matt-blue-rgb: 54, 106, 195;
$matt-blue-light: mix(#fff, $matt-blue, 20%);
$matt-blue-dark: mix(#000, $matt-blue, 20%);

.element {
  color: $matt-blue;
  box-shadow: 0 0 0 2px rgba($matt-blue, 0.35);
}