Overlapping divs

I require 2 overlapping divs, which look like the one below.

    ------------------------------------
   |                      |             |
   |   ------------------ |             |
   |  '                  '|             |
   |  '                  '|             |
   |  '                  '|             |
   |  '                  '|             |
   |  '开发者_开发技巧                  '|             |
   |  '                  '|             |
   |  '                  '|             |
   |  --------------------|             |
   |  '                  '|             |
   |  '                  '|             |
   |   -------------------|             |
   |                      |             |
   |                      |             |
    ------------------------------------

But somehow am unable to get it. here is the place am fiddling out Can anyone tell me where am I going wrong.

Edit 1: I have a left div and a right div. The left div has the overlapping div. Right div is a normal div. I guess most of you are confused and thing the right div to be the overlapping one, there are 2 divs in the left div i need those to overlap.

Sorry to confuse you all.

I think you want something like this:

html

<div class="parent">
  <div class="a"></div>
  <div class="b"></div>
</div>

css

.parent {
  position: relative;
}

.a {
  position: absolute;
  width: 100px;
  height: 100px;
  z-index: 100;
  background: red;
}

.b {
  position: absolute;
  width: 80px;
  height: 180px;
  z-index: 110;
  left: 10px;
  background: blue;
  top: 10px;
}

Edit: in your case parent = contentContainer, a/b = leftContainer/rightContainer

I have changed like this:

#rightContainer {
    /*float:right ;*/
    width:20%;
    /*margin:0px;*/
    margin-top: 30px;
    margin-left: 30px;
    padding:0px;
    position:relative;
    background-color:Lime;
}

You may change the "30px" as you like. I have tested in FireFox only.

You will have to use top, left and z-index properties for that.

Im not really sure how to use the z-index

But i think this might help in the style tag

margin:-50px -50px 0px 0px;

the minus property works, how well it does should be all about testing