zinozzino/index.css

## index.css
.root {
  background-color: yellow;
}

## index.html
<!DOCTYPE html>
<html>
  <head>
    <title>과제</title>
    <link href="./index.css">
  </head>
  <body>
    <div id="root">
      <p>안녕하세요!</p>
    </div>
  </body>
</html>
	<!DOCTYPE html>
	<html>
	<head>
	<title>과제</title>
	<link href="./index.css">
	</head>
	<body>
	<div id="root">
	<p>안녕하세요!</p>
	</div>
	</body>
	</html>