For reference, for anyone reading the thread and looking for how to edit the CSS:
You have two options:
#1: The easiest way is to go to Tools & Plugins > Custom CSS.
#2: The more complex method: Create a theme override, copy the main.css file in assets > css and paste it in your theme override (make sure to also copy the folder structure). Add your CSS overrides and changes here, and make sure to add /* comments */ to keep track of your changes once it comes time to upgrade.
The advantage with method #2 is that you can benefit from the advantages of a code editor when making CSS changes, vs editing your CSS inside of Publii. If you’re making extensive changes and are knowledgeable in CSS, I recommend this method. The downside, though, is that anytime you have to upgrade your theme, you have to do a git diff of your modified CSS file with the latest one to make sure you have all the stylesheet updates you need.