$(document).ready(function() {
$("#coll_bt").click(function(){
$("#coll_list").slideToggle(350);
//$("dl").css = ("z-index","100"); 
//$("ul").css = ("z-index","1"); 
})
 var conf = {
    className : 'btn',
    postfix : '2'
  };
  var image_cache = new Object();
  $('img.'+conf.className).each(function(i) {
    var imgsrc = this.src;
    var dot = this.src.lastIndexOf('.');
    var imgsrc_on = this.src.substr(0, dot) +  conf.postfix + this.src.substr(dot, 4);
    image_cache[this.src] = new Image();
    image_cache[this.src].src = imgsrc_on;
    $(this).hover(
      function() { this.src = imgsrc_on; },
      function() { this.src = imgsrc; });
  });
});