RFR: 8226990: GTK & Nimbus LAF: Tabbed pane's background color is not expected one when change the opaque checkbox. [v12]

[Abhishek Kumar]

On Thu, 2 May 2024 15:07:30 GMT, Tejesh R <tr at openjdk.org> wrote:

>> `unselectedBackground` color is used to render the unselected tabs. What else you want me to check?
>
> I don't see the rendering code in `installDefaults()`, can you recheck that.

`unselectedBackground` was not defined in GTKLookAndFeel class. Although the default graphics color for unselected tab was white but added the required property to make code consistent across LAFs.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17720#discussion_r1588630301