Menu Item Settings > Submenu > Indent Submenu
Indenting a Stacked Submenu
If you would like to create spacial differentiation between your parent and child items in a column stack, you can use the Indent Submenu setting in the Menu Item Settings.
This is can also be useful if you’re stacking multiple groups of items in a single column, or not using column header borders
In the example above, “Indent Submenus” has been enabled on “Best Sellers”, “Drama”, and “SciFi/Fantasy”