#0370B9

CSS

:root {
  --french-blue: #0370b9;
  --french-blue-rgb: 3 112 185;
  --french-blue-oklch: oklch(0.532 0.141 247.8);
}

.element {
  color: var(--french-blue);
  background-color: hsl(204 97% 37%);
  border-color: oklch(0.532 0.141 247.8);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #0370b9;
  --color-french-blue-50: #d7f9ff;
  --color-french-blue-100: #c5ecff;
  --color-french-blue-200: #a6daff;
  --color-french-blue-300: #7dbdfd;
  --color-french-blue-400: #52a4ed;
  --color-french-blue-500: #1d8bde;
  --color-french-blue-600: #1d76bb;
  --color-french-blue-700: #175e96;
  --color-french-blue-800: #084670;
  --color-french-blue-900: #06304f;
  --color-french-blue-950: #001c34;
}

SCSS

$french-blue: #0370b9;
$french-blue-rgb: 3, 112, 185;
$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);
}