<center><form>abc</form></center>
<html> <head> <style type="text/css"> center{border: 1px red solid;} form{border: 1px blue solid; width:40%;} div{border-style: solid; text-align: center;} </style> </head> <body> <center> <form> sss </form> </center> <div> <form> jjjjj </form> </div> </body> </html>