How can I give div a sensitive height

Question

I declare that I am studying responsive design, but there is one thing that I still cannot understand, so far ...

Here is a working example: http://ericbrockmanwebsites.com/dev1/

I would like the div element (contactBg) with the text inside it to go down to the bottom of the image. Obviously, I can do this by defining a height in px, but then this height is maintained when the rest of the window is resized instead of being fluid.

If there are good articles, you may know that this explains how to do this, that would be very helpful, thanks!

Here's the mark up:

<div class="row-fluid">
        <div class="span10 offset1">
            <div class="container-fluid">
                <div class="row-fluid">
                    <div class="span5">
                        <img src="images/logo.jpg" alt="logo" />
                        <img src="images/store.jpg" alt="store" />
                    </div><!-- /span5 -->
                    <div class="span7">
                        <img src="images/portal.jpg" alt="portal">
                        <div class="contactBg">
                            Administration: Emma Jane Julien<br />
                            <a href="mailto:[e-mail]">[e-mail]</a>
                        </div><!-- /contactBg -->
                    </div><!-- /span7 -->
                </div><!-- /row-fluid -->
            </div><!-- /container-fluid -->
        </div><!-- /span10 offset1 -->
    </div> <!-- /row-fluid -->

And here is the css:

   body {
        background: url(../images/3D2A1698A177AF9B71_218.png) repeat;
    }

    img {
        max-width:100%;
        padding-bottom:1%;
    }

     .container-fluid {
        background:#fff;
        padding: 1%;
    }

      .row-fluid {
        width: 100%;
        *zoom: 1;
 }
      .row-fluid [class*="span"] {
        display: block;
        float: left;
        width: 100%;
        min-height: 30px;
        margin-left: 1%;
        *margin-left: 2.709239449864817%;
        -webkit-box-sizing: border-box;
           -moz-box-sizing: border-box;
                box-sizing: border-box;
}

      .row-fluid .span10 {
        width: 82.87292817679558%;
        *width: 82.81973668743387%;
      }

      .row-fluid .span7 {
        width: 58.06353591160195%;
        *width: 57.12912895262725%;
      }

      .row-fluid .span5 {
        width: 40.93646408839753%;
        *width: 40.00205712942283%;
      }
      .row-fluid .span4 {
        width: 31.491712707182323%;
        *width: 31.43852121782062%;
      }

    .contactBg {
        background: #282624;
        padding: 3%;
        max-width:100%;
        height:auto;
    }

Answer 1

, , .

caniuse.com:

: vw, vh, vmin, vmax - CR , 1% (vw), (vh), (vmin) (vmax).

: http://caniuse.com/#feat=viewport-units

div {
/* 25% of viewport */
  height: 25vh;
  width: 15rem;
  background-color: #222;
  color: #eee;
  font-family: monospace;
  padding: 2rem;
}

<div>responsive height</div>

Hide result

Answer 2

div , .

, , 75% 25%.

, , . .contentBg 5.5%.

, Media Queries , , , .

Answer 3

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Answer 4

, VW . : - : 10vw; .