As we've seen in Chapter 1, An Introduction to Ext JS 5, we talked about the folder structure in version 5. We also said that the resources folder disappeared, and in its place, we have now the packages folder. This folder contains many subfolders that are used to build our application and also contains theme folders (CSS, images, SASS, and so on).

Theme folders were reorganized in this version in order to provide a cleaner and organized way to create new themes. Also, we can say that themes were hierarchically constructed. This means that Ext JS themes extend a package in order to be created.

Look at the following diagram to understand how the hierarchy is set for themes:

So, after showing this hierarchy, it's advisable to say that Neptune and Classic are the most frequent themes to be extended to create a custom theme. This is because both of these themes contain all of the necessary code for creating new themes.

Extending the Neutral theme can be considered a very abstract...