Portfolio

 
         <div class="tiled-gallery portfolio">
            <div class="row no-gutter">
                <div class="col-md-12">
                    <div class="col-md-6 wow fadeInUp">
                        <div class="tile tile-1 view overlay hm-blue-light z-depth-2"><a class="waves-effect waves-light"><h5 class="title">Category 1</h5><div class="mask"></div></a></div>
                    </div>

                    <div class="col-md-3 wow fadeInUp" data-wow-delay="0.2s">
                        <div class="tile tile-2 view overlay hm-blue-light z-depth-2"><a class="waves-effect waves-light"><h5 class="title">Category 2</h5><div class="mask"></div></a></div>
                    </div>

                    <div class="col-md-3 wow fadeInUp" data-wow-delay="0.4s">
                        <div class="tile tile-3 view overlay hm-blue-light z-depth-2"><a class="waves-effect waves-light"><h5 class="title">Category 3</h5><div class="mask"></div></a></div>
                    </div>

                    <div class="col-md-3 wow fadeInUp">
                        <div class="tile tile-4 view overlay hm-blue-light z-depth-2"><a class="waves-effect waves-light"><h5 class="title">Category 4</h5><div class="mask"></div></a></div>
                    </div>

                    <div class="col-md-6 wow fadeInUp" data-wow-delay="0.2s">
                        <div class="tile tile-5 view overlay hm-blue-light z-depth-2"><a class="waves-effect waves-light"><h5 class="title">Category 5</h5><div class="mask"></div></a></div>
                    </div>

                    <div class="col-md-3 wow fadeInUp" data-wow-delay="0.4s">
                        <div class="tile tile-6 view overlay hm-blue-light z-depth-2"><a class="waves-effect waves-light"><h5 class="title">Category 6</h5><div class="mask"></div></a></div>
                    </div>

                    <div class="col-md-3 wow fadeInUp">
                        <div class="tile tile-7 view overlay hm-blue-light z-depth-2"><a class="waves-effect waves-light"><h5 class="title">Category 7</h5><div class="mask"></div></a></div>
                    </div>

                    <div class="col-md-3 wow fadeInUp" data-wow-delay="0.2s">
                        <div class="tile tile-8 view overlay hm-blue-light z-depth-2"><a class="waves-effect waves-light"><h5 class="title">Category 8</h5><div class="mask"></div></a></div>
                    </div>

                    <div class="col-md-6 wow fadeInUp" data-wow-delay="0.4s">
                        <div class="tile tile-9 view overlay hm-blue-light z-depth-2"><a class="waves-effect waves-light"><h5 class="title">Category 9</h5><div class="mask"></div></a></div>
                    </div>

                </div>
            </div>
        </div>
        

Changing the background

 
            .portfolio .tile-1 {
                background-image: url(http://mdbootstrap.com/wp-content/uploads/2015/10/kfi5dark.jpg);
            }
            
            .portfolio .tile-2 {
                background-image: url(http://mdbootstrap.com/wp-content/uploads/2015/10/kfi3dark.jpg);  
            }
            
            etc. (.tile-3, .tile-4 ... .tile-9)