#3A6CB5

CSS

:root {
  --matt-blue: #3a6cb5;
  --matt-blue-rgb: 58 108 181;
  --matt-blue-oklch: oklch(0.533 0.127 257.9);
}

.element {
  color: var(--matt-blue);
  background-color: hsl(216 51% 47%);
  border-color: oklch(0.533 0.127 257.9);
}

Tailwind CSS v4

@theme {
  --color-matt-blue: #3a6cb5;
  --color-matt-blue-50: #e0f7ff;
  --color-matt-blue-100: #cfe9ff;
  --color-matt-blue-200: #b5d6ff;
  --color-matt-blue-300: #91b9f9;
  --color-matt-blue-400: #6ea0e9;
  --color-matt-blue-500: #4d86d9;
  --color-matt-blue-600: #4271b7;
  --color-matt-blue-700: #345b93;
  --color-matt-blue-800: #22436d;
  --color-matt-blue-900: #172e4d;
  --color-matt-blue-950: #081b33;
}

SCSS

$matt-blue: #3a6cb5;
$matt-blue-rgb: 58, 108, 181;
$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);
}