This project offers static javascript, css and image files. It bundles well known libraries, e.g. bootstrap, into jar files that can be used in Servlet containers (>= 3.0).
Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window common-font-lato-3.0.0.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.