Board Thread:Support Requests - Designing Your Wiki/@comment-25301601-20140207044730/@comment-2093602-20140207170435

If you just want the background to be transparent and not the text, you can use background-color: rgba(255,0,0,0.5) /* Transparent red */

If you do want the text to be transparent, use  like 2Actimv said. background-color: red; opacity: 0.5;