Why IE7 is not respecting the z-index order?

Question

1. The #cm_sidebarDIV div has z-index 3;
2. The .abouttop and .aboutlist divs have z-index 2

So #cm_sidebarDiv is at the top when it is displayed in Firefox and Chrome but in EI7 it remains at the bottom.

#leftmanulist{ background:url("images/abouttop.gif") no-repeat;
float: left;
margin: 2px 2px 5px 30px;
padding:39px 0 0 0;
width:237px;
}

#leftmanulist ul li{line-height:35px;text-align:left; text-decoration:none;}
#leftmanulist ul li a{ text-decoration:none;}

#leftmanulist ul li:hover{ color:#0068FF;}
#leftmanulist ul li a:hover{ color:#0068FF;}

#leftmanulist ul li.index{ color:#0068FF;}
#leftmanulist ul li.index a{ color:#0068FF;}

  .abouttop{background:url("images/leftmanulist_z.gif") repeat-y ;
    padding:0 6px;  position:relative; z-index:2;
    width:237px;}

    .aboutlist{position:relative;left:28px;}
    .aboutbutton{background:url("images/leftmanulist_b.gif") no-repeat;
    width:237px; height:20px; position:relative; top:-17px; z-index:2;}
    .inword{color:#555555;font-size:0.92em;text-align:justify;line-height:24px;letter-spacing:1px; padding:30px 40px 0px 336px; }


    #cm_sidebarDIV {
        z-index: 3;
    }

Any suggestions?

Answer 1

Set the position explicitly of #cm_sidebarDIV to either relative or absolute.

Answer 2

For z-index to work correctly, it must have a positioning setting different than static, which is the default. Try changing it for relative (or absolute, if thats what you need).

#cm_sidebarDIV {
    position: relative;
    z-index: 3;
}

Answer 3

I think this is one of the mysterious phenomenon of IE. I changed all the about divs to position: static and that solved the problem (not sure why).