How to override the ZKs "div.z-grid-header th.z-column" css?

I need to make the wrap of column headers, as column headers alignment is going beyond limit. So for that I think we need to override "div.z-grid-header th.z-column" CSS class. But if I override the same at page level it is not allowing, throwing exception. I tried to override via ZK.xml as well but no luck. Can anybody help me out?

Solution

<style>div.z-grid-header th.z-column, div.z-grid-header th.z-auxheader{
    white-space:normal;
    }
</style>

This solved my problem !