[lewiscollard]

Then un-mess them up :)

  html {
    filter: invert(1);
  }

  img {
    filter: invert(1);
  }

Bookmarklet edition:

    javascript:(function(){var s=document.createElement("style");s.innerText="html{filter: invert(1);}img{filter: invert(1);}";document.head.append(s)})()

(doesn't and can't fix CSS "background-image" but you'll live)