Dropdown on menu doesn't work properly

I have a dropdown on the menu. On most browsers it seams to be ok, but on Chrome (on my laptop and Desktop) the box looks like this whereas it should look like this.

The problem with it rendering how it does on Chrome is that when the user moves there cursor down to click an option, because they go ‘off’ the dropdown onto the background, the box closes meaning the options are unreachable.

Is there any way I can fix this?