This is more a suggestion than an answer.
From looking at your previous questions, it seems that this button was a problem for you. It seems that your initial question regarding the button did not include Nimbus at all, but it was most likely how to get the look and feel of the button.
I could suggest, instead of trying to tinker with the look and maybe just choose the look that you like. All of the below can be found at sourceforge
SeaGlass LAF

Liquid LAF

There are various LAF files in the JTattoo library that you can choose from
JTattoo Acryl LAF

JTattoo Graphite LAF

JTatto McWin LAF

JTatto Texture LAF

Happy search!
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