WORK IN PROGRESS! making a website is hard. my brain is too small to understand wtf is going on. heres some things that ive struggled with so maybe they can help other people who are new to html.
things that confuse me
sometimes, when updating your site the changes won't apply with hitting the refresh button. using ctrl + F5 you can "force reload"? and that will retrieve all the new stuffs.
img not working?
make sure the full file name, including any folder navigation, is included in the <img src="FILENAME.PNG"> command.
copied/borrowed css code being unexplainably weird?
the code may be using a different language than css. neocities initally gives you .css files, but some code online uses something called .scss which is similar but not quite the same thing. i don't fully understand it myself but most of it effects your nesting. dump the chunk you're having trouble with into SCSS to CSS and see if that helps.