.cont{display:inline-block;width:200px;height:200px;border:1px solid red;position:absolute;left:150px;top:2px;display:none;}

 <div style="border:1px solid green;margin:30px auto;width:150px;" id="menu">

             <div class="item" id="div1" style="position:relative;">

                 <span style="display:inline-block;background: #abcdef;width:150px;height:50px;cursor:pointer;">123</span>

                 <span id="span1"  class="cont">

                      hello1111111

                      hello1111111

                      hello1111111

                      hello1111111

                      hello1111111

                 </span>

             </div>

             <div id="div2" class="item" style="position:relative;">

                 <span style="display:inline-block;background: red;width:150px;height:50px;cursor:pointer;">123</span>

                 <span class="cont">hello222222</span>

             </div>

             <div id="div3" class="item" style="position:relative;">

                 <span style="display:inline-block;background: green;width:150px;height:50px;cursor:pointer;">123</span>

                 <span class="cont">hello333333</span>

             </div>

          </div>

  window.onload = function(){

              var oSpan1 = document.getElementById("span1");

              var oMenu = document.getElementById("menu");

              var oSMenu = oMenu.childNodes;

              for(var n=oSMenu.length-1; n>=0; n--){

                   if(oSMenu[n].className == "item"){

                       oSMenu[n].onmouseover = function(evt){

                             var target = oTargetByClass._get_target_child(this.childNodes, "cont");

                             target.style.display = "block";

                       }

                        oSMenu[n].onmouseout = function(evt){

                             var target = oTargetByClass._get_target_child(this.childNodes, "cont");

                             target.style.display = "none";

                      }

                   }

              } 

              var oTargetByClass = {

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                              return childNodes[i];

                         }

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