Question

I am unable to set z-index. would you please define me, how to set z-index position or values ?

Answer 1

Here is the code and example to try:

http://www.w3schools.com/cssref/tryit.asp?filename=trycss_zindex

Just enter the test value for z-index and other properties and test immediately how it behave.

Added more info

z-index for image is defined as below:

img
{
 position:absolute;
 left:0px;
 top:0px;
 z-index:-1;
}

There are two thing which you can modify with respect to z-index:

position: absolute  | relative | fixed
z-index: +ve | -ve value from -9999 to 9999

In the above example you can change the values in real time to see the effect which will help you to understand it much better.