CSS on TextButton not working properly

I'm working on a project which was made using GWT components but now I want to change to GXT components.

For some reason the CSS doesn't work properly on my GXT TextButtons.

Button:

TextButton test = new TextButton("Test");

test.setStyleName("testStyle");

Result

nd8S8.png

As you can see, the css is applied but only around the button. Have I missed something?