Basic geometry consists of edges and faces
A face is always bounded by edges - it cannot exist without them.
But edges can exist without any face associated with them.
I said to select the face an reverse its orientation.
Unless you select a face there's no 'Reverse' in the context-menu.
Selecting an edge on its own won't do what you want...
'Flat' edges will style with the styled-geometry facing up.
If an edge bounds a face, then the face's orientation determines which way the styled-geometry faces - that's why reversing a face affects how its new styling appears.
If an edge is shared by more than one face then the face that's most squarely oriented onto the camera is used for the orientation of the styling...