topp{

    
            position: absolute;
            background-color: white ;
            height:64px;
            top:0;    
            left:50%;            
            width:501px;                
            margin-left: -250px;             

            }            
            #topp span{
                display:inline-block;                
                width:100px;                
                font-size:24px;
                height:32px;                    
            }
            希望每行显示5个，却四个就掉下了了width设为550倒是可以，却又空出50px...