#big_button1{
    display: block;
    position: absolute;
    top: 117px;
    _top: 117px;
    left: 293px;
    _left: 305px;
    width: 170px;
    height: 160px;
    background: url(../images/b10.png) top left no-repeat;
  }

  #big_button1:hover{
    background: url(../images/b11.png) top left no-repeat; 
  }

  #big_button2{
    display: block;
    position: absolute;
    top: 117px;
    _top: 117px;
    left: 613px;
    _left: 620px;
    width: 170px;
    height: 160px;
    background: url(../images/b20.png) top left no-repeat; 
  }

  #big_button2:hover{
    background: url(../images/b21.png) top left no-repeat; 

  }