MUMUP-1152 : minor issue with overlap on short screens

### Before 

![image](https://cloud.githubusercontent.com/assets/3534544/4508152/1eef2baa-4b13-11e4-9ec3-5db5265f8c3f.png)

### After
![image](https://cloud.githubusercontent.com/assets/3534544/4508160/2e370f56-4b13-11e4-902f-de10d4dd7042.png)


Knowledge : overflow of divs can be an issue if you use relative.