Good evening Stefan and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the difference in styles you bumped into.
I would love to help you with this topic.
What is going on is that the shortcode version of the calendar is drawing from the CSS rules of your WordPress theme, while the basic calendar is using the CSS rule of the Events Calendar.
The good news is that you can fix this:
- Head over to Events -> Settings -> Display and under Default stylesheet used for events templates, choose “Full styles”
- Decide which look you prefer and add the missing CSS rules to your custom CSS box
Let me know how that goes.
Best regards,
Geoff B.