change modal dialog css for more than button

the old style keep the same, but no it works vor more than 2 buttons

befor:
![before](https://cloud.githubusercontent.com/assets/165599/3078174/ac50d95e-e460-11e3-85e6-119024f5496c.jpg)

after:
![after](https://cloud.githubusercontent.com/assets/165599/3078178/c9768344-e460-11e3-8b65-82b30603d6d9.jpg)