#1770B2

CSS

:root {
  --french-blue: #1770b2;
  --french-blue-rgb: 23 112 178;
  --french-blue-oklch: oklch(0.53 0.13 247.1);
}

.element {
  color: var(--french-blue);
  background-color: hsl(206 77% 39%);
  border-color: oklch(0.53 0.13 247.1);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #1770b2;
  --color-french-blue-50: #d9f9ff;
  --color-french-blue-100: #c7ecff;
  --color-french-blue-200: #a9d9ff;
  --color-french-blue-300: #82bdf7;
  --color-french-blue-400: #59a5e7;
  --color-french-blue-500: #2c8bd7;
  --color-french-blue-600: #2876b5;
  --color-french-blue-700: #205f92;
  --color-french-blue-800: #11466c;
  --color-french-blue-900: #0b304c;
  --color-french-blue-950: #001c32;
}

SCSS

$french-blue: #1770b2;
$french-blue-rgb: 23, 112, 178;
$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);
}