Answering my own question –
For the simple things, just go to Appearance->Customize. At the bottom is “Additional CSS”.
Add your code in the editor provided.
For something more complex, including creating a child theme or editing css in the child theme (or in the original theme, against all advice from those who know), a variety of file manager plug-ins will provide access to all files in the WP installation. I picked Filester – File Manager Pro because it looked like it would provide the access I need (and it did).
Thanks, but my question is can I access those files from the dashboard? I know how to edit if I log into the host server (or FTP the files, edit, and FTP them back).
