We have created a new module, that allows you to have a nice offcanvas mobile menu within Cassiopeia.
This module takes care of the quirky looking mobile menu from the default cassiopeia template and replaces it with an offline canvas menu. Highly configurable, and easy to setup.
A decent 404 page is quite important. This error means that a certain page is not found. If you do not make your own 404 page, the error you will see is quite technical and can scare off your visitors. Cassiopeia has ha 404 page, but you can create your own if you want to.