function showLoading() {

        document.getElementById("over").style.display = "block";

        document.getElementById("layout").style.display = "block";

    }

 function removeLoading() {

        document.getElementById("over").style.display = "none";

        document.getElementById("layout").style.display = "none";

}

.over {

            display: none;

            position: absolute;

            top:;

            left:;

            width: 100%;

            height: 100%;

            background-color: #f5f5f5;

            opacity: 0.5;

            z-index:;

        }

.layout {

            display: none;

            position: absolute;

            top: 40%;

            left: 40%;

            width: 20%;

            height: 20%;

            z-index:;

            text-align: center;

        }

<div id="over" class="over"></div>

<div id="layout" class="layout"><img src="../../images/loading.gif" alt=""/></div>