this is div 1:

this is div 2:

this is div 3:

this is an empty table with a border-bottom:

this is a table with an empty cell with a border-bottom:

<p>this is div 1:</p>
<div></div>

<hr>

<p>this is div 2:</p>
<div id="d2"></div>

<hr>

<p>this is div 3:</p>
<div id="d3"></div>

<hr>

<p>this is an empty table with a border-bottom:</p>
<table id="t1"></table>

<hr>

<p>this is a table with an empty cell with a border-bottom:</p>
<table>
    <tr>
        <td></td>
    </tr>
</table>

div {
   -moz-box-sizing: border-box;
   box-sizing: border-box;
   background-color: transparent;
   border: 10px solid transparent;
   border-bottom-color: black;
   width: 0!important;
   height: 0!important;
   clear: left;
   }
#d2 {
   display: table;
   border-collapse: collapse;
   }
#d3 {
   display: table-cell;
   border-collapse: collapse;
   }