I get your point: there are no CSS stylesheets or style elements on MathPages at all. Thus, no styles...
The thing is, there are no pages that use no styling! Defaults are styling: they are just choices the browser manufacturer made. Resetting those has its own cottage CSS industry: https://meyerweb.com/eric/tools/css/reset/
I used to view default browser styles as not really styles. Then recently I started trying to use old HTML elements, like 'align', as a way to see if they behaved differently (solved problems with) CSS styling. It turned out that in Safari, Chrome and Firefox, the attributes behaved the same as setting CSS styles -- which makes sense from an underlying architecture point of view (why have two ways to set, say, left alignment?) but shows that the engines are CSS-based, that there is no such thing as not using styles, even using non-CSS, old-fashioned pre-CSS HTML.
