background-size: contain

This page requires either a Gecko-based browser whose rendering code is no older than the last day or so of July 2009 (based off trunk code at that time in mozilla-central) or a browser with support for the unprefixed CSS 3 background properties. Other browsers are not supported either because I don't know they exist or because their background-size support, prefixed or otherwise, doesn't match the latest spec, and I'd rather avoid possible confusion.

Try resizing this page, and watch what happens to the page's background image. This page has the following CSS specified for the body element (NB: distinct from the area containing this explanatory text):

  background-image: url(cowbell.jpg);
  background-attachment: fixed;
  background-repeat: no-repeat;
  background-size: contain;
  -moz-background-size: contain;

The background image is this image, displayed at original size, from the Wikimedia Commons; see COPYING for usage details:

Feel free to take a look at the rest of my site while you're here.