Newbie: What are these distracting diagonal lines? Why are they visible or useful? How do I hide them?

Thanks all. I’ll try to go deeper into that component and practice and learn these things you all suggested.

Asked here Separately:

Side question: Is it possible to add / use a simple existing pattern via Sketchup Web Free tier? If so how?

https://help.sketchup.com/en/layout/filling-shapes-colors-and-patterns

Cant seem to replicate this? Is there separate HELP guide for Web Free version?

Keep running across this UI difference when I google for any How to…do. and then have to trouble you folks on forums.