Thank you for using our theme can you please do share us your URL.
If you want to customize CSS only then you can use Additional CSS in Customizer. You should NEVER modify theme or plugin directly. Otherwise it will be lost when theme is updated. Another alternative is using child theme. https://codex.wordpress.org/Child_Themes
Regarding logo, CSS you have changed is correct. But please keep it in Additional CSS box in the Customizer.
Hi – I am having the same issue with the logo sizing – it is incredibly small in the Business Pro version. I tried adding the custom CSS but it’s not working. Unsure if I am using the custom CSS correctly. See https://www.meetingpointseminars.com