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.