darkmode.js

const darkModeMediaQuery = window.matchMedia('(prefers-color-scheme: dark)')

handleDarkmode(darkModeMediaQuery)

function handleDarkmode(e) {
  const darkModeOn = e.matches; // true if dark mode is enabled

  if (darkModeOn) {
    // TODO: Set Dark Theme
  } else {
    // TODO: Set Light Theme
  }
}

darkModeMediaQuery.addListener(handleDarkmode);