98.css – A design system for building faithful recreations of old UIs

I don't know if anyone else remembers this but in the late 90s, Microsoft had built-in CSS named colours that matched the Windows desktop theme/colours.

I have no idea if these still work (my IDE seems to say they do not, because everything is red).

    body {
      font-size : 11px ;
      color : windowtext ;
      background-color : appworkspace ;
    }
    a {
      color: menutext;
    }
    .headerBar {
      border-top    : 1px solid threedlightshadow ;
      border-left   : 1px solid threedlightshadow ;
      border-bottom : 1px solid threedshadow ;
      border-right  : 1px solid threedshadow ;
      background-color : threedface ;
    }

So you could build web UIs that matched the user's Desktop look and feel. We did this for our browser-based Intranet applications in 1998, which made them look a bit more "native".