<ul>

  <li class="left">abc</li>

  <li class="middle" id="middle" >

    def

    <div>

      <ul style="border:1px solid red;">

        <li>l1</li>

        <li>l1</li>

        <li>l1</li>

      </ul>

    </div>

  </li>

  <li class="right">hjk</li>

</ul>

ul{

  list-style-type: none;

}

.left, .middle,.right{

   float:left;

    width:120px;

    border:1px solid red;

    margin-right:2px;

    position:relative;

}

ul li#middle > div

{

  box-sizing: border-box;

  position:absolute;

  display:block;

  left:-10%;

  width:120%;

  top:100%;

  margin-top:4px;

  border:2px solid green;

}