[Typo3] Trying to get submit button of the mailform to get classed to its own class

[Vlatko Šurlan]

I've place the following ts into the setup field of my root template:
# Separating css class for submit button
tt_content.mailform.20 { params.submit = class = "csc-form-submit" }

But this has the effect of the mailform not showing at all. How can I 
tell typo to put the submit button to its own css class? I use the 
following extensions: css_styled_content, automaketemplate, htmlcssstyling.