Question: zk how to change theme?
Answer: Download the preferred theme. jar file or obtain by maven. Default theme (Breeze or Iceblue) - built-in theme, no need to download and register. ... 
Place theme. jar file under "projectName/WEB-INF/lib" folder.
Apply preferred theme by a library property in zk.xml file under "projectName/WEB-INF" folder.