For First Question , Not realy! with sx props , you can work with The theme , it's look like MUI System with sx props ,change the theme for that specific component 2- For second Question , MUI Using Utility Classes behind the scenes , you can track them with dev tools , MUI manage almost every thing with Utility Classes , But you must consider that , MUI using React and The React it self is not that SEO friendly!

For Better SEO Compatibility , I recommend to use some framework like Tailwind because this framework it can be only dev-dependency , and the final result is only CSS , of course for more animation you need some other frameworks like motion , but however in animation MUI is not that good

But if for something like first initializing the page , use SSR , SEO of your website will be fine