Center single circle on second row

Hi all!

I love the spun theme, thanks Caroline!
Despite being a beginner, I have managed to modify quite a bit of the theme thanks to the threads on this forum: https://www.karinmodigh.eu

However, there is one thing I can’t find an answer to:
On the entry page I have four circles in two rows, with three in the upper and one in the lower. But I want the single circle in the lower row to be centered. How do I fix that?

I use Custom CSS Manager.

Thank you very much for your help!
Karin