Syntax highlight theme on Files tab

[extrawurst]

Discussed in https://github.com/extrawurst/gitui/discussions/1928

^{Originally posted by VasilisManol October 18, 2023} Hi,

Is there a way to change the theme used in Files tab for syntax highlighting? It is unreadable on any terminal with light background. The rest of the GUI is rendered nicely on a light terminal. It is just the opened file under Files and only on light background that is very pale and unreadable.

[extrawurst]

actually good point. this is currently controlled by syntect default theme. this should be possible to overwrite with a separate highlighting theme