Please don’t tell anyone..ha..but I still don’t know how those child theme thingy works and I never wanted to spend the time to learn. Awful huh..I know.
Anywho – I know about exactly which part I change in the styles.css – mainly add borders to image and gallery – change menu position to be below the logo (I use long logos like 700px generally so I push the menu below) – this type of things so I can find those parts easily. Besides the css I also alter the header for the same reason – menu position – don’t like the menu on the right..sorry 🙂 that’s about it. The other parts can be done in the backend with customize.