Hi @Fleur_Alleman,
It seems the solution for the issue with the rounded corners is in your previous topic, you can find it here: Rounded border in Team showcase widget 
As for the number counter widget inside the popup, there is a way to do so! You just need to add HTML block in your Popup widget and add the installation code of your Number Counter widget there. Just in case, here’s an article to help you with that: HTML block in Popup widget - Elfsight Help Center.
Let me know if it helped!