Board Thread:Support Requests - Getting Technical/@comment-4151266-20151104041249/@comment-1757994-20151106094737

 td[style *= "width: 100%;"] * { width: inherit; height: auto; }
 * in Common.css

 then  .banner-wrapper { width: 100%; }
 * (optional) in Template : Notice
 * in Common.css (instead of the suggestion above)

.banner-wrapper * { width: inherit; height: auto; } (MediaWiki translates align= and width= to the correct CSS, but you really don't need text-align here.)

For the user page, you'd then do 

If you don't like "banner-wrapper" for the class name, feel free to choose a different one.

For the background, it's possible to have JavaScript detect the window size and pick an appropriately-sized background image, but a better way is just use CSS to set the background properties and scale the image.

For example  body { background-image: url('http://images.wikia.com/world-war-2/images/5/51/Wiki-background.png'); background-size: cover; } which works for Monobook. The background of the Oasis skin is provided by the skin based on File:Wiki-background (no .png).