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<!-- Preloader -->
<div class="mask"><div id="loader"></div></div>

<!-- CSS -->
/* PAGE PRELOADER
======================================*/
.mask {
    background-color: #fff;
    width: 100%;
    height: 100%;
    position: fixed;
    z-index: 100000;
}

#loader {
    background: url(../img/loader.gif) center center no-repeat;
    height: 50px;
    width: 50px;
    left: 50%;
    top: 50%;
    position: absolute;
    margin: -25px 0 0 -25px;
}

<!-- JAVASCRIPT -->
//Page Preloader
$(window).on('load', function () {
  $("#loader").delay(400).fadeOut();
  $(".mask").delay(600).fadeOut("slow");
});