I am not quite sure when the problem began, but at some point I noticed that the tabs do not look good when I run Netbeans in Fedora. and they look like in this screenshot.
This was happening for sure in Fedora 24 and I see it again in Fedora 25, with both NetBeans 8.1 and 8.2. Initially I dismissed it as a cosmetic annoyance, but at times it became a problem because it is not easy to select the tabs anymore. I tried to find the root of the problem and it seems to be linked to the GTK theme that comes with Fedora. Because Fedora 25 was just around the corner, I decided to wait till the new version is out. Unfortunately, it’s the same in Fedora 25. When I discovered this, I did a bit more googling and I finally found this page describing the same problem and suggesting to specify the Look and feel using the –laf option in command line. For example, if you want to select the Nimbus look and feel you need to run the following command in the terminal:
/usr/local/netbeans-8.2/bin/netbeans --laf Nimbus
whereas for Metal look and feel you need to run (obviously):
/usr/local/netbeans-8.2/bin/netbeans --laf Metal
Just make sure you do not specify the –laf option if you start netbeans from the terminal. If you do, the option is disabled. Embarrassingly simple.