<div 
  id="theMainDiv"
  style="
    border:solid 1px gray;
    cursor:text;
    width:400px;
    padding:0px;"
>
  <span 
    id="tag1_outer" 
    style="
      background:#e2e6f0;
      padding-right:4px;
      padding-left:4px;
      border:solid 1px #9daccc;
      font:normal 11px arial;
      color:#3c3c3c"
  >as</span>
</div>

By default, the will align to the bottom-left corner of the

#theMainDiv {
  height: 20px; /* Set the div height for reference */
}

#tag1_outer {
  line-height: 20px;
}

#theMainDiv {
  position: relative; /* Apply relative positioning to the div */
}

#tag1_outer {
  position: absolute;
  top: 50%;
  margin-top: -10px; /* Half the height of the child span */
}