<script src="https://unpkg.com/react@16/umd/react.development.js" crossorigin></script> code example
Example: react html cdn
<script crossorigin src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>