position:fixed;实现
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>返回顶部</title> </head> <body style="margin: 0"> <div style=" 50px;height: 50px;background-color: aquamarine; position: fixed; bottom: 20px; right: 20px; ">返回顶部 </div> <div style=" 100%;height: 5000px;background-color: antiquewhite">sfsf</div> </body> </html>