Show trash icon on expo completely

The trash icon on the window-close area was displayed too large; fixed it in CSS.

Fix for linuxmint/Cinnamon#3674

![screenshot from 2014-11-26 16 09 30](https://cloud.githubusercontent.com/assets/5564491/5203421/cefd1992-7586-11e4-96a5-5826cc1e2e10.png)