Difficult to see, if the button is active ?

Is it possible to change the Colors of the Buttons in the upper right Corner, because it is very difficult to recognize if they are active (Grey) or inactive (Grey) ?

You would have to create a custom ExtJS theme to modify the color.

Sorry Anton,

I am on a beginner level. So I don't understand your reply. What means ExtjS theme ?

I would recommend to check official documentation:

https://docs.sencha.com/extjs/6.2.0/guides/core_concepts/theming.html