#1871AF

CSS

:root {
  --french-blue: #1871af;
  --french-blue-rgb: 24 113 175;
  --french-blue-oklch: oklch(0.531 0.125 245.5);
}

.element {
  color: var(--french-blue);
  background-color: hsl(205 76% 39%);
  border-color: oklch(0.531 0.125 245.5);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #1871af;
  --color-french-blue-50: #daf9ff;
  --color-french-blue-100: #c7edff;
  --color-french-blue-200: #aadaff;
  --color-french-blue-300: #82bdf4;
  --color-french-blue-400: #5aa5e3;
  --color-french-blue-500: #2d8cd3;
  --color-french-blue-600: #2877b2;
  --color-french-blue-700: #205f8f;
  --color-french-blue-800: #11466a;
  --color-french-blue-900: #0b314b;
  --color-french-blue-950: #001d31;
}

SCSS

$french-blue: #1871af;
$french-blue-rgb: 24, 113, 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);
}