Apply any font of any color, size and font decoration you need. Use any available type, color and thickness of a menu's frame. Choose any color for submenus and items backgrounds. Specify various values for spacing and padding for the whole menu and for each separate submenu. Create separators using your own pictures, size and alignment.
Press "Edit Properties..." button to edit button edges width. By default, when you add new button, its edges widths are set to 5. But if you will change preview button size to 100x50 or bigger, you will see that some image elements look "fuzzy" (left image on the picture below). It happened because the play buttons border is not within the edge area.
Set both horizontal and vertical edges width to 10. You can see that the result looks much more precise now. Border is not resized because it is within the edge area now (right image on the picture above).
Click "Save theme" button to save theme changes. Click "Close" button.