Style:
      ul { 
            padding:0;
            border-spacing:-1px;
            flow: "a a"
                  "b c"
                  "d c";  
            width:*;      
            height:*;
         }
      li { display:block; border:1px solid; width:*; height:*;}
      li:nth-child(1) { float:"a"; }
      li:nth-child(2) { float:"b"; }
      li:nth-child(3) { float:"c"; }
      li:nth-child(4) { float:"d"; }