Hi,

That is coming from Oomph, which has style included from style.config. I will fix that one because background-color:none; really is not valid.

However, there are other things that the validator doesn't like, some CSS 3 (which is not yet a standard) and some vendor specific stuff like -moz and -webkit. These things are useful and work even if they are not technically valid. I think I'm going to disable the css validator link by default going forward because it is really a tool to help find real problems in CSS not a merit badge and the fact that we don't validate 100% is more a condition of the times and technology than something to be seen as a failure. We use what is useful and works and would only be held back by trying to always validate 100%.

The new File Manager UI for example uses some CSS 3 and vendor specific stuff as does the new admin toolbar implemented in the included skins.

However, you have complete control over what css is used, if you want to leave out Oomph or any of the css we include by default in style.config you are free to remove it or change it if 100% CSS validation is a requirement for a given project.

For more info see The Great CSS 3 Validation Debate.

Best,

Joe