*{                margin: auto;                padding: 0px;            }            #a1{                width: 100px;                height: 50px;                border: 1px solid red;            }            #a2{                width: 50px;                height: 50px;                border: 1px solid red;            }            #a3{                width: 100px;                height: 50px;                border: 1px solid red;            }            #a4{                width: 100px;                height: 50px;                border: 1px solid red;            }            #a5{                width: 100px;                height: 50px;                border: 1px solid red;            }            #a6{                width: 100px;                height: 20px;                border: 1px solid red;            }            #a7{                width: 100px;                height: 40px;                border: 1px solid red;            }                                    
     
            
              
     
        
     
            
              
     
        
     
            
              
     
        
     
            
              
     
        
     
            
      
                       计算结果