Fixing items on mobile screen size and menu on desktop size

I need help adjusting a few items on one page of my site on mobile view. And also to check why the menu items are not properly displayed if checking the page as Mac OS user.
On Windows 10, the items appear on top of a white box, but on Mac OS they appear below it, not sure why (the menu issue is affecting all pages except the homepage).

Could you please help me fixing this?