The Struts2 Tags come with the notion of packaged themes or templates. These packaged themes are not meant for changing the display of presentation, but enables a developer to align the package or theme selection, with the HTML presentation implementation (CSS, AJAX, XHTML, or even old school, simple HTML).
In addition the Struts2 Tag library comes with the ability to override the default package implementations provided. Some of the default packaged themes may perform as desired, but in some instances, you may have to customize the tags display output.
Below, I've provided two great starting points in helping you overload your templates and customizing the behaviour of your Struts2 tags.