@Haikal, sorry to bother you, I think I figured it out.

For any other newbs, if you get this error, you need to add the <dependency> block at http://mvnrepository.com/artifact/org.eclipse.jetty/jetty-server/9.3.7.v20160115 into the <dependencies> section of the pom.xml file in the logback-demo directory and then run the mvn package jetty:run command again.

Does this need to be fixed at http://logback.qos.ch/demo.html?

Thanks, all.