Gotcha. Judging by the aliasing on your screenshot, it looks like you're using the designer on a screen with a partial DPI scale (i.e. 125% or 150%). Historically all DPI scaling has been a problem for Java; it's better now than it was, but still has issues with fractional scale factors. If you're able to, I'd recommend either disabling the scale factor or disabling it for the designer via a JVM argument: