I am trying to create a child theme of an existing installed theme in order to do some customization. I am not that familiar with WordPress, but I am familiar with web development in general. This is a one-click install of wordpress.
First I tried simply creating the minimal files needed for the child theme in wp-content/themes/newtheme. To do this I ssh'd into my server and added a style.css and functions.php. When I do it this way the new theme isn't shown in the list on the Appearance > Themes page. I can use wp-cli to activate it, but my child theme's style.css file 404s when the browser requests it. Directly requesting style.css in any of the adjacent theme directories works fine though.
I also tried uploading a theme zip file from within wp-admin, which worked, but I can't find the files anywhere on the server after uploading them, which means I can't continue to update the theme files via SSH or FTP as needed.
What am I missing here? How can I get a child theme into this install that can be managed via FTP/SSH?