#0F71B1

CSS

:root {
  --french-blue: #0f71b1;
  --french-blue-rgb: 15 113 177;
  --french-blue-oklch: oklch(0.53 0.129 245.3);
}

.element {
  color: var(--french-blue);
  background-color: hsl(204 84% 38%);
  border-color: oklch(0.53 0.129 245.3);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #0f71b1;
  --color-french-blue-50: #d8f9ff;
  --color-french-blue-100: #c6edff;
  --color-french-blue-200: #a8daff;
  --color-french-blue-300: #80bef6;
  --color-french-blue-400: #56a5e6;
  --color-french-blue-500: #268cd5;
  --color-french-blue-600: #2377b4;
  --color-french-blue-700: #1c5f91;
  --color-french-blue-800: #0e466b;
  --color-french-blue-900: #09314b;
  --color-french-blue-950: #001d32;
}

SCSS

$french-blue: #0f71b1;
$french-blue-rgb: 15, 113, 177;
$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);
}