How to make an object go to a higher layer

I want this to be on top... how can I do this and not have it go underneath...

http://opentech.durhamcollege.ca/~intn2201/brittains/chatter/sig开发者_运维百科nup_step2.php

I think there is a way in CSS to make stuff go on higher layers I think I read something about it a few years ago but I forget what its called.

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z-index