Doesn't quite work sorry, end up looking like this:
They're horizontal now, but are slightly left aligned, underneath the Heading to the left which is odd.
Trying to make the dropdown menus show horizontally rather than vertically, but also have each submenu show underneath it's top level. All the code i've tried either formats it to right or centre alignment but not under the menu it's related to (which works when it's set as the standard vertical option).