* Make sure the path is correct which is $XDG_CONFIG_HOME/wofi/style.css
(XDG_CONFIG_HOME defaults to $HOME/.config if it is unset).
* Try to specify it manually with -s option from the terminal and see if
it works or gives any errors.
Other than that, I have no idea. I also installed it same as you and it works
fine on my machine.
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Best Regards, Oğuz