#1F70B1

CSS

:root {
  --french-blue: #1f70b1;
  --french-blue-rgb: 31 112 177;
  --french-blue-oklch: oklch(0.531 0.127 247.8);
}

.element {
  color: var(--french-blue);
  background-color: hsl(207 70% 41%);
  border-color: oklch(0.531 0.127 247.8);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #1f70b1;
  --color-french-blue-50: #daf9ff;
  --color-french-blue-100: #c8ecff;
  --color-french-blue-200: #abd9ff;
  --color-french-blue-300: #84bdf6;
  --color-french-blue-400: #5da4e5;
  --color-french-blue-500: #338bd5;
  --color-french-blue-600: #2d76b4;
  --color-french-blue-700: #245e91;
  --color-french-blue-800: #14466b;
  --color-french-blue-900: #0d304b;
  --color-french-blue-950: #011c32;
}

SCSS

$french-blue: #1f70b1;
$french-blue-rgb: 31, 112, 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);
}