I can also assure you, CSS and choice of UI framework is the absolute least of your priorities over business development, marketing, revenue generation, and sec

I can also assure you, CSS and choice of UI framework is the absolute least of your priorities over business development, marketing, revenue generation, and security holes. Unless, of course, people find the design of your MVP so utterly boring that they dislike the product entirely. I don't believe that design can be treated as an optional feature, that it's something you can add on later.