JAVASCRIPT

detect browser theme

if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
  console.log('User prefers dark mode on his device');
}

detect browser theme

@media (prefers-color-scheme: dark) {
  // color variables for users which want your site to be dark
}
@media (prefers-color-scheme: light) {
  // color variables for users which want your site to be light
}