Thread:Project:Support desk/How to edit skins without access to the file/reply

That's where you place CSS code to override the default CSS code.

You can view the default css code in the file skins/vector/screen.css (as well as skins/common/commonInterface.css, skins/common/commonContent.css and skins/common/commonElements.css) on your install. However, please do not edit these files. It will break things, particularly if you ever update your MediaWiki install. Instead put any css you want to override into MediaWiki:Common.css