确保较大分区中两个分区之间的线一直延伸到父分区的底部

div background-color

  #left,
  #right {
    width: 40%; /* adjust to taste */
    float: left;
    padding: 1em; /* adjust to taste */
  }
  #left {
    border-right: 4px solid #000; /* adjust to taste */
  }
  #right {
    border-left: 4px solid #000;
    margin-left: -4px; /* the negative width of the border */
  }

JS Bin Demo

  #left,
  #right {
    width: 40%;
    float: left;
    padding: 1em;
  }
  #left {
    border-right: 4px solid #000;
  }
  #right {
    border-left: 4px solid #000;
    margin-left: -4px; /* the negative width of the border */
  }

  #right p,
  #left p {
    border-left: 1px solid #ccc;
    border-right: 1px solid #ccc;
    margin: 0;
    padding: 0 0.5em 1em 0.5em;
  }

  #right p:first-child,
  #left p:first-child {
    padding-top 1em;
    border-top: 1px solid #ccc;
  }

  #right p:last-child,
  #left p:last-child {
    border-bottom: 1px solid #ccc;
  }

Demo at JS Bin

:last-child #left #right

<div id="wrap">
    <div id="left">
        <div class="innerWrap">
            <!-- content -->
        </div>
    </div>
    <div id="right">
        <div class="innerWrap">
            <!-- content -->
        </div>
    </div>
</div>

  #left,
  #right {
    width: 40%;
    float: left;
    padding: 1em;
  }
  #left {
    border-right: 4px solid #000;
  }
  #right {
    border-left: 4px solid #000;
    margin-left: -4px; /* the negative width of the border */
  }

  div.innerWrap {
    border: 1px solid #000;
  }

Demo at JS Bin

divitis

http://www.kensfi.com/set-a-div-height-equal-with-of-another-div/

if (get(div1).offsetHeight > get(div2).offsetHeight( {
  div1.borderRight = 1px;
else
  div2.borderLeft = 1px;