10-styling.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>10-styling</title>
    <style>
      .box {
        display: flex;
        margin: 1rem;
        align-items: center;
        padding: 1rem;
        box-sizing: border-box;
        flex-direction: row;
        border: 1px solid #555555;
        justify-content: center;
      }
      .box--small {
        width: 8rem;
        height: 4rem;
      }
      .box--medium {
        width: 12rem;
        height: 6rem;
      }
      .box--large {
        width: 24rem;
        height: 12rem;
      }
    </style>
  </head>
  <body>
    <div id="root"></div>

    <script src="https://unpkg.com/react@16.7.0/umd/react.production.min.js"></script>
    <script src="https://unpkg.com/react-dom@16.7.0/umd/react-dom.production.min.js"></script>
    <script src="https://unpkg.com/@babel/standalone/babel.min.js"></script>

    <script type="text/babel">
      const rootEl = document.getElementById("root");

      const Box = ({ children, size, style }) => {
        const sizeClassName = size ? `box--${size}` : null;

        return (
          <div
            className={`box ${sizeClassName}`}
            style={{ fontStyle: "italic", ...style }}
          >
            {children}
          </div>
        );
      };

      const contentEl = (
        <>
          <Box size="small" style={{ backgroundColor: "lightblue" }}>
            Small box
          </Box>

          <Box size="medium" style={{ backgroundColor: "pink" }}>
            Medium box
          </Box>

          <Box size="large" style={{ backgroundColor: "orange" }}>
            Large box
          </Box>
        </>
      );
      ReactDOM.render(contentEl, rootEl);
    </script>
  </body>
</html>