.cuadradito{
  background-color: #f00;
  height: 50px; 
  width: 50px;
  margin:3px;
  z-index: -1;

}

#divmensaje {
   background-color: yellow;
   position: absolute; 
   visibility: hidden; 
   padding: 5px;
   width:250px;
   z-index: 100;
}