JQuery :: Change Z-index Is Not Permanent?

I have some code for one of my websites that when you click on a image button, it makes a div's z-index change and thus it disappears, revealing another div underneath it. However, when you click on any link in the page then, the first div reappears to cover the hidden div. Basically, how can i make it so jquery changes the z-index permanently (until the user refreshes the page)?

Here's my code:

*exitOutWelcome is the class of the button I'm clicking
*#top is the div that disappears by having it's z-index changed.
<script> // Change z index....
$(".exitOutWelcome").click(function(){
$("#top").css('z-index','-1');
});