#1F6FB3

CSS

:root {
  --french-blue: #1f6fb3;
  --french-blue-rgb: 31 111 179;
  --french-blue-oklch: oklch(0.53 0.13 249.1);
}

.element {
  color: var(--french-blue);
  background-color: hsl(208 70% 41%);
  border-color: oklch(0.53 0.13 249.1);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #1f6fb3;
  --color-french-blue-50: #daf9ff;
  --color-french-blue-100: #c8ecff;
  --color-french-blue-200: #abd9ff;
  --color-french-blue-300: #84bcf8;
  --color-french-blue-400: #5da4e8;
  --color-french-blue-500: #338ad8;
  --color-french-blue-600: #2d75b6;
  --color-french-blue-700: #245e92;
  --color-french-blue-800: #14456d;
  --color-french-blue-900: #0d304c;
  --color-french-blue-950: #011c33;
}

SCSS

$french-blue: #1f6fb3;
$french-blue-rgb: 31, 111, 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);
}