Edit the CSS code of installed wordpress.org layout

Hello! I have installed and already added pages to the Wordpress.org layout McLuhan layout found here (https://wordpress.org/themes/mcluhan/) to my own domain. I need someone to change the CSS code to make a few changes to the design.

I need the code to be clean, easy to understand, and accessible. I will only choose you if you have a good track record with editing Wordpress CSS code for clients and very good reviews. Please see my (very wonderful) image for a clearer understanding of what I require.