#2870AE

CSS

:root {
  --french-blue: #2870ae;
  --french-blue-rgb: 40 112 174;
  --french-blue-oklch: oklch(0.531 0.12 248.4);
}

.element {
  color: var(--french-blue);
  background-color: hsl(208 63% 42%);
  border-color: oklch(0.531 0.12 248.4);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #2870ae;
  --color-french-blue-50: #dcf9ff;
  --color-french-blue-100: #cbecff;
  --color-french-blue-200: #aed9ff;
  --color-french-blue-300: #88bcf3;
  --color-french-blue-400: #62a4e2;
  --color-french-blue-500: #3b8bd2;
  --color-french-blue-600: #3376b1;
  --color-french-blue-700: #295e8e;
  --color-french-blue-800: #194569;
  --color-french-blue-900: #10304a;
  --color-french-blue-950: #031c31;
}

SCSS

$french-blue: #2870ae;
$french-blue-rgb: 40, 112, 174;
$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);
}