Why the sub-navigation is hidden behind the slider advertisement lay under IE?

HTML & CSS
1 
http://idealmobile.gomoxy.net/version1/

when your mouse hover on the ACCESSORIES, the sub-navigation hide behind the slider advertisement lay under IE, i have set the slider lay, z-index:99; the sub-navigation z-index:9999;but it doesn’t work

2

Try this:

.header-container {
  position: relative;
  z-index: 100;
}
3

it’s ok. many thanks. could you tell me what’s the reason causing this.

4

It’s a bug in older versions of IE. You have to set a higher z-index on the container of the menu than of the container of the slider. It’s explained in some detail here in other posts, such as here:

5