When having the option set that the menu is next to the logo, in some cases the menu aligns left, interfering with the logo.
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.
To set the background-color for your mobile menu please read this article!
Using the color slider to setup your colors in various options of our module is something you will do often. How to use this is explained in this article.
Joomla (and Joomla 4) itself has the option to work with tabs in your content. This tutorial will explain how this works.