<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <style> .box { width: 100px; height: 100px; /*补全代码*/ position:fixed; top:0; left:0; background-color:yellow; } </style> </head> <body> <div class='box'></div> <script type="text/javascript"> /* 填写JavaScript */ </script> </body> </html>