Hmm… Looks like you are being bitten by my workaround for dark themes there…

Could you please test this quick test hack and see if it works better in your case:
https://storage.ninetailed.ninja/index.php/s/uvvqFd6oPIhNFzB

Also please state which operating system, desktop environment & browser version your are using. If applicable also add information about your system desktop theme.

To respond please open an issue on https://gitlab.com/alexander255/user-agent-switcher/issues as I will not receive any notifications when you update your review. Thanks!