Split an image into left and right parts and fill the browser

Question

I'm trying to split an image into a left and right side. I did this but I want the div to be centered and fill the browser so the images are edge to edge and be responsive. Right now it's all flush to the left.

I put a border so you can see that it's in fact two images put together to make one - 600x900 each.

JSFIDDLE: https://jsfiddle.net/omarel/vnc522vu/3/

HTML

 <div id="centercontainer">


 <div id="scrollablecontainer">

    <img id="leftside" class="halfCompositionLeft" src="https://dl-web.dropbox.com/get/pool_left.jpg?_subject_uid=9047713&w=AAC25lQ4ebCI8ajjRKwfi_TANvxEYQruCRN5PQDEEZ70Uw">


    <img id="rightside" class="halfCompositionRight" src="https://dl-web.dropbox.com/get/pool_right.jpg?_subject_uid=9047713&w=AABZnKZrODSr9rGU5kOX7q2EHycNMAqq-mvlUxn0T5tVAg">


    </div>

 </div>

CSS:

.scrollableSectionContainer section>img {
    position:absolute;
}

.centercontainer {
  margin: 0 auto;
  overflow: hidden;
  top: 0%;
  right: 0%;
  width: 100%;
  height: 100%;
  opacity: 0;
  position: relative;
}

.scrollablecontainer {
  position: absolute;
  top: 0%;
  left: 0%;
  width: 100%;
  height: 100%
}

   .halfCompositionLeft {
    position:absolute;
    top:0px;
    left:0px;
    width:600px;
    height:900px;       
}
.halfCompositionRight {
     position: absolute;
     top: 0px;
     left: 600px;
     width: 600px;
    height: 900px;
    border:#FFF solid thin; 
 }

Answer 1

Try this:

#halfCompositionLeft{
    position: absolute; //Absolute Positioning.
    top: 0px; //Top of the page.
    left: 0px; //Leftmost side.
    width: 50%; //Fill half the page.
    height: 100%; //Fill page vertically. 
}

#halfCompositionRight{
    position: absolute; //Absolute Positioning.
    top: 0px; //Top of the page.
    left: 50%; //Start halfway through the page.
    width:50%; //Fill rest of page.
    height: 100%; //Fill page vertically. 
}

That uses CSS percentages rather than pixel values, which dynamically sets size and position based on page size. To complete this, simply make the full box 100% wide and 100% high, and it will fill the page appropriately.

EDIT: CSS for placing div parallel underneath:

#halfCompositionLeft2{
    position: absolute; //Absolute Positioning.
    top: 100%; //Similar, but at the bottom of the page, under the top div.
    left: 0px; //Leftmost side.
    width: 50%; //Fill half the page.
    height: 100%; //Fill page vertically. 
}

#halfCompositionRight2{
    position: absolute; //Absolute Positioning.
    top: 100%; //Similar, but at the bottom of the page, under the top div.
    left: 50%; //Start halfway through the page.
    width:50%; //Fill rest of page.
    height: 100%; //Fill page vertically. 
}