Update oxid.css

This is a pull request in b-dev-ce for this topic:
https://github.com/OXID-eSales/oxideshop_ce/pull/156
I had put it in the wrong branch.

It fixes a bug with the z-index of the facebook-like-button-flyout. It changes two z-indexes. It keeps the file cloudzoom.js unchanged. @Mantas, thank you for your help!