You can undo things by going to the top right of your screen and clicking the three-dot button, then find undo. Or by clicking CTRL + Z or ALT + DEL
You can stop yourself from accidentally deleting things on a page by locking it. You can lock a page from the same menu I mentioned in the last tip
If you are wondering how I got the font to look like this I did that by going to the menu I mentioned then enabling Small Text, Full Width, and using the Serif font (The default font is too boring in my opinion and Serif looks more fun)