html - Div still has height:0px -

i have div has content still has height:0px;, in example can see "index-slideshow" has height:0px; , need "position:absolute;" because photos must 1 above other jquery slideshow.

this div has contents hasn't height. what's problem?

jsfiddle demo

#index-slideshow {    margin: 0px;    position: relative;    width: 100%;    padding: 0px;    max-width: 100%;    box-sizing: border-box;    z-index: -1;  }  #index-slideshow > img {    position: absolute;    top: 0px;    left: 0px;    width: 100%;    max-width: 100%;    margin: auto;    box-sizing: border-box;  }  .wrap {    margin: 0 auto;    width: 950px;    max-width: 93%;    border: 0px;    padding: 0px 10px 10px 10px;    background-color: blue;    color: white;  }

<div id="index-slideshow">    <img src="http://lorempixel.com/400/200">    <img src="http://lorempixel.com/g/400/200">  </div>  <div class="wrap">    <p>lorem ipsum dolor sit amet, consectetur adipiscing elit. pellentesque suscipit magna ...      </p>  </div>

it because, 2 images inside <div> has position: absolute;. absolutely positioned elements not take space.

see example here:

.border {border: 1px solid #999; margin-bottom: 100px;}  .abs {position: absolute; height: 50px; width: 50px; background-color: #ccc;}

<div class="border">    <div class="abs">i absolute!</div>  </div>  <div class="border">    hi    <div class="abs">i absolute!</div>  </div>

it impossible calculate height of absolutely positioned elements, css, because not in layout.

either make position of images static or give min-height.