Added 100% width to open dropdown menus on mobile
What does this MR do?
Sets dropdown-menus to be 100% width on small screens.
Are there points in the code the reviewer needs to double check?
Do we want this on all dropdown menus or only dropdown menus activated by full-width buttons? /cc @dzaporozhets
Why was this MR needed?
What are the relevant issue numbers?
Closes #18858 (closed).