#066FBD

CSS

:root {
  --french-blue: #066fbd;
  --french-blue-rgb: 6 111 189;
  --french-blue-oklch: oklch(0.532 0.147 249.7);
}

.element {
  color: var(--french-blue);
  background-color: hsl(206 94% 38%);
  border-color: oklch(0.532 0.147 249.7);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #066fbd;
  --color-french-blue-50: #d7f9ff;
  --color-french-blue-100: #c5ecff;
  --color-french-blue-200: #a6d9ff;
  --color-french-blue-300: #7ebcff;
  --color-french-blue-400: #52a3f1;
  --color-french-blue-500: #1f8ae2;
  --color-french-blue-600: #1e75bf;
  --color-french-blue-700: #185d99;
  --color-french-blue-800: #094572;
  --color-french-blue-900: #063050;
  --color-french-blue-950: #001c36;
}

SCSS

$french-blue: #066fbd;
$french-blue-rgb: 6, 111, 189;
$french-blue-light: mix(#fff, $french-blue, 20%);
$french-blue-dark: mix(#000, $french-blue, 20%);

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