CSS modules make sure that your CSS is locally scoped by adding a unique hash to your classnames. You will understand it better once we use CSS modules for styling our random number generator...

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It is possible to use React without any toolchain and integrate it directly into your existing website by using simple tags. Using toolchains will speed up your development, give you access to some additional features and allow you to detect mistakes in your code. The feature of Create React App is the ability to use CSS modules.

Learn React 18: Using CSS Modules