CSS z-index paradox flower

Question

I would like to create a paradoxical effect via the z-index CSS property.

In my code I have five circles, like in the image below, and they are all absolutely positioned with no defined z-index. Therefore, by default, every circle overlaps the previous one.

Right now, circle 5 overlaps circle 1 (left image). The paradox I'd like to achieve is to have, at the same time, circle 1 under the circle 2 and on top of circle 5 (as in the right image).

_{(source: schramek.cz)}

Here's my code

Markup:

<div class="item i1">1</div>
<div class="item i2">2</div>
<div class="item i3">3</div>
<div class="item i4">4</div> 
<div class="item i5">5</div>

CSS

.item {
    width: 50px;
    height: 50px;
    line-height: 50px;
    border: 1px solid red;
    background: silver;
    border-radius: 50%;
    text-align: center;
}

.i1 { position: absolute; top: 30px; left: 0px; }
.i2 { position: absolute; top: 0px; left: 35px; }
.i3 { position: absolute; top: 30px; left: 65px; }
.i4 { position: absolute; top: 70px; left: 50px; }
.i5 { position: absolute; top: 70px; left: 15px; }

A live example is also available at http://jsfiddle.net/Kx2k5/.

I tried a lot of techniques with stacking orders, stacking context and so on. I read some articles about these techniques, but no success. How can I solve this?

Answer 1

Here's my attempt: http://jsfiddle.net/Kx2k5/1/
(successfully tested on Fx27, Ch33, IE9, Sf5.1.10 and Op19)

---

CSS

.item {
   /* include borders on width and height */  
   -webkit-box-sizing : border-box;
   -moz-box-sizing    : border-box;
   box-sizing         : border-box;
   ...
}

.i1:after {
   content: "";

   /* overlap a circle over circle #1 */
   position : absolute;
   z-index  : 1;
   top      : 0;
   left     : 0;
   height   : 100%;
   width    : 100%;

   /* inherit border, background and border-radius */
   background    : inherit;
   border-bottom : inherit;
   border-radius : inherit;

   /* only show the bottom area of the pseudoelement */
   clip          : rect(35px 50px 50px 0);
}

Basically I've overlapped an :after pseudoelement over the first circle (with some properties inherited), then I've clipped it with clip() property, so I only make its bottom section visible (where circle #1 overlaps the circle #5).

For the CSS properties I've used here, this example should be working even on IE8 (box-sizing, clip(), inherit, and pseudoelements are supported there)

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Screenshot of resulting effect