Please follow the given steps to restore your default theme in NetBeans.
Step 1: Open your NetBeans IDE.
Step 2: Now go to the very left corner and click on “NetBeans” and you will small drop-down menu and here click on “Preferences” option.
Step 3: Once you click on the “Preferences” option in step-2 you will see the following window. Here you have click on the “Appearance” Tab and then select the option “Mac OS X” in drop-down box as shown in given image below.
Then click the ‘Apply’ button below.
Step 4: Once you click on the “Apply” button. You will see a pop notification that will ask you to click and restart IDE to restore the default theme of NetBeans IDE. Please click and restart IDE.
Once the restart is done your IDE is ready with the default theme as you are willing to do.
If you guys have any doubts, please feel free to ask in the comment box. I will try my best to solve your issue as soon as possible.
Thanks for reading.