GTKLookAndFeel defines the UI properties "TitledBorder.border" as an EtchedBorder with default highlight/shadow colors. These colors are calculated as brighter/darker versions of the background, instead of getting them from the current theme.

More seriously, the UI properties "TitledBorder.titleColor" and "TitledBorder.font" are hard-coded in GTK L&F, causing the title to be rendered in small black text on a very dark background when using the HighContrastLargePrintInverse theme.
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