How to create your buttons, skins, toolbars and UI!
If you run the editor with the default UI, which is written in React, then adding a button will be straightforward. Buttons are standard React classes. For your convenience, there is also a number of mixins, which you can use that provide basic functionality out of the box. Then, use CKEditor's API to do style the content and that is it!
AlloyEditor bundles a couple of gorgeus skins that you can use out of the box. However, if you need a better integration with your app's look and feel, you can easily create your own skin.
Adding a new toolbar is also as straightforward as adding a button.