The short answer is: Yes, you will need to use CSS for React. There are different ways that you can incorporate CSS into your React app, including using inline styles, using a Css-in-Jss approach, or using a pre-processor such as Sass.
As such, when building an app with React, you will need to write CSS to define how the React components should be stylized. This can be done by writing your own custom CSS stylesheets and linking them to your React components. You can also use a pre-processor such as Sass or Less to easily create and maintain complex sets of styles.
Inline styles are another way to provide styling to React components. This involves writing styling directly in the JSX code and applying those styles to the elements. This approach is best used for simple styling, as more complex styling will become hard to maintain.
As you can see, CSS is an important part of React, and you will need to incorporate it in your projects in one way or another. Whether you prefer to write your own CSS stylesheets or use a pre-processor such as Sass or Less, or use inline styles or the CSS-in-JS approach, there is an option available to suit your needs. No matter which approach you take, make sure that your applications are well-styled and easily maintainable in the long term.