The end result has to be some combination of HTML, CSS, and JavaScript; otherwise, your browser really won’t know what to do. Now, here’s where the special nature of React comes in.

Facebook found that initial principles of React Native—serving as a single asynchronous, serializable, and batched bridge between JavaScript and native apps—made it harder to build features.

CSS: Enter CSS to be applied to the HTML used in your tests. It is placed between <style> elements in the header portion of the page. HTML: This area allows you to enter HTML to be used in your tests.