Hey @Michel,
This is unfortunately not possible with some extensive code customization. Are you comfortable with customizing code?
While we cannot help with custom code, we do have a knowledgebase article that covers a lot of the basics of how you might go about making this sort of change. You can check that article out here: https://theeventscalendar.com/knowledgebase/themers-guide/.
I hope that helps; let me know what further questions you might have based on this initial information! 🙂
— George