Sure but doing that sets the style across the entire site. What if I wanted some parts to have one style and others a different style. Like if the Header was in the style of Roger, the sidebar in the style of Mona and the main body the style of Anna?
What do you mean do it manually. Where would one do it manually? In the customizer the only place I can set the style is the Main Style which is across the entire site not specific parts of the site.