Portlet style is not generated on exoPlatform

I create a simple portlet. I test on tomcat7. And this is the capture.

Then, I want to install it to eXoplatform. I follow this tutorial (
Use Vaadin with eXo Platform and Build Stunning Web Applications

The problem is: The style of it’s button doesn’t work. This is the capture.

After inspecting and compare, I found that on the second result, the ‘http://localhost:8080/html/VAADIN/themes/quicknote/styles.css’ is not generated by vaadin.

Why ?

Thanks for any advice.