Hi Johan,
It looks like the widget is being affected by some theme styles or something else, which is doing that. As outlined in our forum guidelines, we aren’t able to help with these kinds of customization issues. But we do have some handy resources that might be helpful for you:
▪ Themer’s Guide – provides an overview of how to customize the plugin’s frontend appearance.
▪ Tutorials – useful tips and tricks for changing how the plugin looks and behaves.
▪ Technical Docs – provides an overview of the classes and functions in each plugin
Good luck, and thanks for using The Events Calendar!
~Leah