#0571B3

CSS

:root {
  --french-blue: #0571b3;
  --french-blue-rgb: 5 113 179;
  --french-blue-oklch: oklch(0.531 0.133 245.3);
}

.element {
  color: var(--french-blue);
  background-color: hsl(203 95% 36%);
  border-color: oklch(0.531 0.133 245.3);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #0571b3;
  --color-french-blue-50: #d8faff;
  --color-french-blue-100: #c5edff;
  --color-french-blue-200: #a7daff;
  --color-french-blue-300: #7ebef8;
  --color-french-blue-400: #53a5e8;
  --color-french-blue-500: #208cd8;
  --color-french-blue-600: #1f77b6;
  --color-french-blue-700: #195f92;
  --color-french-blue-800: #0a466c;
  --color-french-blue-900: #07314c;
  --color-french-blue-950: #001d32;
}

SCSS

$french-blue: #0571b3;
$french-blue-rgb: 5, 113, 179;
$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);
}