Change the dark mode theme for a portable appimage? (chromium browser)

[Tesla-Tank]

I'm trying to figure out if there's a way to change the default theme on a chromium browser to a different type. I have a custom theme used on kde that syncs well with it, but the default gtk and classic theme are still too bright for me. I prefer to have my config portable for my flash drive and made a home folder for it.
So far, I've created a .themes folder within the home directory and the .local/share directory with no luck. Thanks.

[probonopd]

Hello @Tesla-Tank. Run your Chromium AppImage like this: Your.AppImage --appimage-portable-home once. Then do your theme modifications, they should be saved inside the Your.AppImage.home folder alongside the AppImage.

[Tesla-Tank]

I think I originally messed up by creating both the config and home folder. I just made the home folder like you said and saw the config folder within it and placed my gtk theme in it with no problem. Thank you.

[probonopd]

Instead of --appimage-portable-home you could also try --appimage-portable-config (but remove the Your.AppImage.home folder first). Depending on where in the home Chromium saves these things, it might be sufficient.

[Tesla-Tank]

That works too. Right now I'm trying to figure out how to change the qt theme to a dark one for the retroarch appimage without external programs.

[probonopd]

This would likely involve extracting and changing the contents of the AppImage (with --appimage-extract).

If you just want to change the colors, setting a custom Qt stylesheet on the application might do the trick. I have not tested this, but something like https://gist.github.com/Advik-B/55a352145bc818f9f02e8695d1132157 might possibly work. You need to tell Qt to load it. I haven't done extensive research but so far I haven't found a way to do this without recompiling the application.

Alternatively, you'd need to bundle a Qt style and its dependencies, then repack as an AppImage (using appimagetool).

So, it seems like with the default style in Qt, these are not just settings, but code changes.

[Samueru-sama]

You need to tell Qt to load it. I haven't done extensive research but so far I haven't found a way to do this without recompiling the application.

It is possible and I make use of it.

I usually have this on my Qt appimages: https://github.com/pkgforge-dev/puddletag-AppImage/blob/main/puddletag-appimage.sh#L60-L61

It checks if there is a file with the name of the AppImage + .stylesheet, if so it sets the env variable APPIMAGE_QT_THEME to that file.

After that it checks again if the variable contains a valid file, if this is true it runs set -- "$@" "-stylesheet" "$APPIMAGE_QT_THEME" which passes the Qt theme to the array.

If you wonder why I then check the variable, this is because the user can also set the variable to point to a stylesheet file anywhere they want and that way if they have several Qt appimages they all make use of the same .stylesheet file.

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Something crazy is that i have not been able to find documentation about the -stylesheet flag. I learned about this because some user shared it with me.

[probonopd]

Didn't know about the -stylesheet flag, exactly what I was looking for, thanks for sharing @Samueru-sama!