51help TIY
码：
<!DOCTYPE html> <html> <head> <style> [class|=top] { background:yellow; } </style> </head> <body> <h1 class="top-header">Welcome</h1> <p class="top-text">Hello world!</p> <p class="content">Are you learning CSS?</p> <p><b>注释：</b>对于 IE8 的 [attribute|=value] <!DOCTYPE>。</p> </body> </html>
查看结果: