添加正确的类以使 H1 元素变为红色。
<!DOCTYPE html>
<html>
<head>
<style>
.mystyle {color:red;}
</style>
</head>
<body>
<h1 @(15)>My Home Page</h1>
</body>
</html>
<!DOCTYPE html>
<html>
<head>
<style>
.mystyle {color:red;}
</style>
</head>
<body>
<h1 class="mystyle">My Home Page</h1>
</body>
</html>
<!DOCTYPE html>
<html>
<head>
<style>
.mystyle {color:red;}
</style>
</head>
<body>
<h1 class='mystyle'>My Home Page</h1>
</body>
</html>