Mobile menu not showing child pages and issue with subpage menu styling

I’m working on a client project and they asked to make some content changes their website and add some pages. I’m a designer, not a developer, but this kind of basic stuff I can generally do. When I added child pages to the menu I ran into 2 issues:

  1. The last child page in the list would have a box around it (like the button styling for the website). I cannot find the CSS that is doing this (at least I’m guessing it is CSS doing it)

  2. When in mobile view, the menu item won’t expand to show the child pages. I’ve turned the submenu toggle on, and the little down arrow shows up, but you can’t click it to expand to actually see the child pages. I don’t know if this is a CSS issue either (maybe menu height?)

I’ve looked in all the places I know of for CSS (and that Google told me) Tools>Global Settings; Tools>Layout CSS and Javascript; Customize>Additional CSS. The only location I haven’t looked is Appearance>Editor to find the styles.css and that’s because there is not Editor tab under Appearance in the wordpress menu (and I do have Administrator access). Appreciate any help or advice