HTML 标题（Heading）是通过 <h1> - <h6> 等标签进行定义的
<!DOCTYPE HTML> <html> <body> <h1>This is heading 1</h1> <h2>This is heading 2</h2> <h3>This is heading 3</h3> <h4>This is heading 4</h4> <h5>This is heading 5</h5> <h6>This is heading 6</h6> <body> </html>
效果如下：
This is heading 1
This is heading 2
This is heading 3
This is heading 4
This is heading 5
This is heading 6