Alert box close button inherits background color

When using a button for the alert-box close button, the background would be a different color than the color of the alert box.

![foundation_fix](https://cloud.githubusercontent.com/assets/2957492/4537554/04c6686e-4ddf-11e4-80a8-f9e82f76f413.PNG)

This fixes that and makes it blend in.