Aigelov

.all_pr li {
  float: left;
  margin: 5px 10px;
  position: relative;
}

var drop_down = $('.demo .drop-down');
	
if ( drop_down.length > 1 )
{
	drop_down.on('click', function()
	{
		$('.all_pr > li').css(
			{
				'z-index' : 0
			}
		);
		$(this).parent().parent().closest('li').css(
			{
				'z-index' : 1
			}
		);
	});
}