As you can see in attached screenshots Unity Editor is full of this kind of interface graphic bugs. I am using Ubuntu 18.04 with LXDE and this happens on desktop environments other than default GNOME desktop environment. I am pretty sure there are many Linux users not using Gnome. I wish if there was a chance of Unity developer team making Unity compatible with other desktop environments. Since Gnome is slow many Linux user prefer other DE's. That would be great if Unity were compatible with other DE's. Though I know that your developer team's main aim is making Unity stable as possible, that would be nice to at least think about making unity compatible with other DE's. I also wonder if anyone else encountered with same problem. Also I made a pool to see if who uses GNOME or not. Feedback appreciated. Note: I reported this bug and got a kind and quick response. Thanks for support. I am opening this thread because I want to raise interest in this situation. I hope this is the right place to do it.
This looks like a similar problem that another user posted in this form using KDE. The issue is that we'd like to support all window managers, but we have a very limited amount of support resources. Linux is a bit challenging as different window managers can introduce entire concepts that other WMs don't have, and the combinations of software+distro can really explode the matrix we need to test. We choose to support Gnome at this time only as it's the default WM for our supported distros. However KDE is a huge runner up, so I'd like to get this working better in KDE so it's at least not completely broken.
Is looks very much like compositing is not enabled on your window manager. Many 3D games and applications (not just Unity) require compositing to render properly. On KDE there is an option in the settings to enable the compositor. I'm sure there is an equivalent in LXDE. You might want to try that. Edit: I'm using Unity on KDE and I don't have this problem.