Just upgraded to Beta 3 and noticed that there are issues with the sidebar. The reading list icon, import and extras icons have disappeared and the top item in the Favourites is obscured by the top UI element of the sidebar
In addition the Inspector appears to be missing UI elements as well - such as the buttons for switching between generic and custom info views.
Not seeing any issues here.
What OS and does it persist after rebooting the machine?
Looks fine over here too (and beta 3 didn’t even change the sidebar/inspector icons or their handling).
Rebooting seemed to sort the issue out. I should have known better 
Rebooting often solves a host of ills. 