White sub-menu and texts on mobile

Hi, I found this problem where the sub-menu and texts on mobile are completely white and this causes a big problem for my users who are navigating through my website. However, this occurs at every page including newly created pages onward, except for the home, about and gallery pages.

I’ve tried adding different css codes that I’ve found on the forums but to no avail. Is there a solution to this? I’m using the free Astra theme if it helps.

Would appreciate it if I can get the css codes for the sub-menu background and text colours, as well as the main menu border colours if possible.