Page identifier

Hello,

My template uses different css for active/non active menu. eg for homepage as I seen uses the function is_home(). Is there any identifier that I can use for togling the active/inactive css?
To be honest I did some tries, eg usings if qa_script() but the only that I got where errors. I was using for year vBulletin and they have something like THIS_SCRIPT == 'xxxxx'. Is there something similar here?

Thank you
Chris