While it's possible to implement mobile-first React user interfaces by rolling your own CSS, I would recommend against doing this. There are a number of CSS libraries that handle the seemingly endless edge cases for you. In this section, I'll introduce the react-bootstrap package—React components for Bootstrap.
The react-bootstrap package exposes a number of components that serve as a thin abstraction layer between your application and Bootstrap HTML/CSS.
Let's implement some examples now. Another reason I'm showing you how to work with react-bootstrap components is that they're similar to react-native components, which you'll learn about starting in the next chapter.
The idea with the following examples is not in-depth coverage of react-bootstrap, or Bootstrap itself for that matter. Rather, the idea is to give you a feel for what it's like to work with mobile-first components in React by passing them state from containers and so on. For now, take a look at the react-bootstrap documentation (http://react-bootstrap.github.io/) for specifics.