Child css file not working

I created a “sixteen-child” theme folder in the way I normally do and activated it. I added footer and home pages to it and made minor updates to those, and those work fine. I also added a “style.css” file to the folder, but it’s NOT working. I do not like making changes to the main.css for obvious reasons (updates will override). Making changes in Sixteen Settings>Layout Settings>Custom CSS is also not working. This is really slowing me down, because I want to make only minor changes to the display: lose the capital letter on page titles and the “Home” nav bar display. I also want to make the post “featured images” of flexible depths (i.e., whatever I need so I get a zig-zaggy grid of links to event descriptions inside. And I want to shut off display of the featured image on the post page (found code for that elsewhere on this site). Maybe change a few colors. Can anyone help??!!