Thread:Project:Support desk/Making a new tag

I would like to make a new tag, how do I do it? For example, if I wanted to say make a tag, which would make all text in the tag in italics, bold, and green, what code would I have to do for it? Can I link it to CSS? I don't know how to do this stuff. MediaWiki version: 1.19.2 PHP version: 5.2.17 (apache2handler) MySQL version: 5.1.61