Hi, Caroline.
Thanks for the screenshots. This appears to be your theme’s styling taking over the Community Events styling.
Could you please provide a link to your Community Events “Add New” form (and provide login credentials in a Private Reply if Anonymous Submissions is not enabled)?
This will let me see what styling is being applied (again, likely from your theme) so I can point you in the right direction to get this resolved (e.g. switch themes, contact the theme author to resolve, or implement some custom CSS to fix it).
However, please understand that, per our Scope of Support / Terms, we do not provide styling or theme integration support so I likely won’t be able to provide you the full fix for whatever styling is affecting the form. I’ll do my best to help point you in the right direction though.