Child Theme Suddenly Completely Broken

I made a child theme for a small organization a few months ago. It’s located here:

Current Version

The theme is completely broken either after updating my theme or WordPress itself. I’m trying to determine what has actually changed but I see no easy method of doing this besides manually comparing each line of HTML/CSS to a previous version available at Archive.org:

Archived Version

Is there anything obvious that is overwriting all my styling tags or do I have to manually compare all these? There obviously seems to be something minor that is overwriting a full stylesheet somewhere or changing some IDs or class names but I don’t have much time to dedicate to this. I’m hoping the issue jumps out at somebody familiar with themes.