I surrender, oh mighty CSS

I give up.  Just spent the last hour or two screwing with the mobile menu on my Minecraft site. It looks great on a computer, and it works fine on mobile. Ran into one weird issue that I just CAN’T seem to fix.  On mobile, if you drop down a sub-menu, it works great.  If there are a lot of items in the sub-menu, you get these super weird large rounded corners around the whole thing.

I can’t fix it. I’ve tried everything. I even got the plugin to modify the settings for that menu directly, and it still does it.  Only options left are to fully replace the menu (which wouldn’t go with my theme), or just accept it.

So I surrender.