#1F70AF

CSS

:root {
  --french-blue: #1f70af;
  --french-blue-rgb: 31 112 175;
  --french-blue-oklch: oklch(0.53 0.124 247.1);
}

.element {
  color: var(--french-blue);
  background-color: hsl(206 70% 40%);
  border-color: oklch(0.53 0.124 247.1);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #1f70af;
  --color-french-blue-50: #dbf9ff;
  --color-french-blue-100: #c9ecff;
  --color-french-blue-200: #abd9ff;
  --color-french-blue-300: #85bdf5;
  --color-french-blue-400: #5da4e4;
  --color-french-blue-500: #338cd3;
  --color-french-blue-600: #2d76b2;
  --color-french-blue-700: #245f8f;
  --color-french-blue-800: #15466a;
  --color-french-blue-900: #0d304b;
  --color-french-blue-950: #011c31;
}

SCSS

$french-blue: #1f70af;
$french-blue-rgb: 31, 112, 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);
}