Resizing category selection and details box in the event form

Hey there, I am trying to style the form to add a new event a bit, but I am encountering two flaws which I cannot fix:

1. the categories selection shows 10 rows even if I have only 3 active categories; I would like to reduce it at 3 rows if possible, because it looks very ugly right now;

2. the box to add event details overflows the other elements’ width by a good 10-15 pixels on the right.

both the issues are visible here: https://www.lindiependente.it/aggiungi-il-tuo-evento/

thank you in advance!

https://www.ads-software.com/plugins/events-manager/