.preloader-wrapper { 
    background: rgba(22, 22, 22, 0.3); 
    width: 100%; height: 100%; 
    position: fixed; 
    top: 0;
    left: 0;
    z-index: 10;
}

.preloader-wrapper > .preloader { 
    background: transparent url(https://graphiclineweb.files.wordpress.com/2013/10/ajaxloader.gif?w=604) no-repeat center top;
    position: absolute;
    min-width: 128px; /* image-width of loader */
    min-height: 128px; /* image-height of loader */
    box-sizing: border-box;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    padding-top: 148px; /* 128px image-height of loader + 20px margin */
    text-align: center;
}

<div class="preloader-wrapper">
    <div class="preloader">
       Loading...<br/>
       And whatever you want to have here.
    </div>
</div>