#2370AF

CSS

:root {
  --french-blue: #2370af;
  --french-blue-rgb: 35 112 175;
  --french-blue-oklch: oklch(0.531 0.123 247.8);
}

.element {
  color: var(--french-blue);
  background-color: hsl(207 67% 41%);
  border-color: oklch(0.531 0.123 247.8);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #2370af;
  --color-french-blue-50: #dbf9ff;
  --color-french-blue-100: #c9ecff;
  --color-french-blue-200: #acd9ff;
  --color-french-blue-300: #86bcf4;
  --color-french-blue-400: #5fa4e3;
  --color-french-blue-500: #368bd3;
  --color-french-blue-600: #3076b2;
  --color-french-blue-700: #265e8f;
  --color-french-blue-800: #17466a;
  --color-french-blue-900: #0f304b;
  --color-french-blue-950: #021c31;
}

SCSS

$french-blue: #2370af;
$french-blue-rgb: 35, 112, 175;
$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);
}