First of all many thanks for the Abook Extension.
I have some questions.
Firstly, I translated the extension to German completely (All Language Files). Since I had to go through all the entries, I found bugs in CSS style.
I found display errors in Joomla Administrator in the ADMIN Views Singular (Edit). Example when opening new book. The tooltips are not all the same, they have two different styles. Once it's in black color and once it's in white color (that's not the problem). The problem is this variant of white, one can not read because it is obscured by the browser border (window). The position is not good. Tooltips You can not read in any browser.
Testet in Joomla and Browser:
Joomla Version 3.8.8
Joomla Version 3.8.10
Last Version Firefox
Last Version Chrome
Microsoft Edge
Microsft IE 11
The second question is: Do you think about further developing the extension for Joomla 4?
I have screenhots here:
Many Thanks
Rene