Bookmarklet - Dark mode code.

cwest-dark-mode.bookmarklet.js

(()=>{
  const docElem = document.documentElement;
  const FILTERS = [
    "",
    "invert(1) hue-rotate(180deg) contrast(0.75)",
    "invert(1) contrast(0.75)",
    "invert(1) hue-rotate(180deg)"
  ];
  const VAR_NAME = "cwestDarkMode";
  const DATA_VAR_NAME = `data-${VAR_NAME.replace(/[A-Z]/g, '-$&').toLowerCase()}`;
  
  let filterIndex = docElem.dataset[VAR_NAME];
  filterIndex = filterIndex
    ? (+filterIndex + 1) % FILTERS.length
    : +(localStorage.getItem(VAR_NAME) || 1);
  docElem.style.filter = FILTERS[filterIndex];
  
  // Store the data in local storage and in the docElem.
  docElem.setAttribute(DATA_VAR_NAME, filterIndex);
  localStorage.setItem(VAR_NAME, filterIndex);
})();

https://www.yourjs.com/tools/js-minifier/?input=js&output=bookmarklet&label=Dark+Mode