Add loading overlay for ajax requests

css/main.css

@@ -765,3 +765,68 @@ select option:disabled {
     color:lightblue;
     border-color:blue;
 }
+
+.sk-cube-grid {
+  width: 60px;
+  height: 60px;
+  position: fixed;
+  top: 50%;
+  left: 50%;
+  transform: translate(-50%, -50%);
+}
+
+.sk-cube-grid .sk-cube {
+  width: 33%;
+  height: 33%;
+  background-color: #4527A0;
+  float: left;
+  -webkit-animation: sk-cubeGridScaleDelay 1.3s infinite ease-in-out;
+          animation: sk-cubeGridScaleDelay 1.3s infinite ease-in-out; 
+}
+.sk-cube-grid .sk-cube1 {
+  -webkit-animation-delay: 0.2s;
+          animation-delay: 0.2s; }
+.sk-cube-grid .sk-cube2 {
+  -webkit-animation-delay: 0.3s;
+          animation-delay: 0.3s; }
+.sk-cube-grid .sk-cube3 {
+  -webkit-animation-delay: 0.4s;
+          animation-delay: 0.4s; }
+.sk-cube-grid .sk-cube4 {
+  -webkit-animation-delay: 0.1s;
+          animation-delay: 0.1s; }
+.sk-cube-grid .sk-cube5 {
+  -webkit-animation-delay: 0.2s;
+          animation-delay: 0.2s; }
+.sk-cube-grid .sk-cube6 {
+  -webkit-animation-delay: 0.3s;
+          animation-delay: 0.3s; }
+.sk-cube-grid .sk-cube7 {
+  -webkit-animation-delay: 0s;
+          animation-delay: 0s; }
+.sk-cube-grid .sk-cube8 {
+  -webkit-animation-delay: 0.1s;
+          animation-delay: 0.1s; }
+.sk-cube-grid .sk-cube9 {
+  -webkit-animation-delay: 0.2s;
+          animation-delay: 0.2s; }
+
+@-webkit-keyframes sk-cubeGridScaleDelay {
+  0%, 70%, 100% {
+    -webkit-transform: scale3D(1, 1, 1);
+            transform: scale3D(1, 1, 1);
+  } 35% {
+    -webkit-transform: scale3D(0, 0, 1);
+            transform: scale3D(0, 0, 1); 
+  }
+}
+
+@keyframes sk-cubeGridScaleDelay {
+  0%, 70%, 100% {
+    -webkit-transform: scale3D(1, 1, 1);
+            transform: scale3D(1, 1, 1);
+  } 35% {
+    -webkit-transform: scale3D(0, 0, 1);
+            transform: scale3D(0, 0, 1);
+  } 
+}

index.html

@@ -96,6 +96,20 @@
         </div>
     </div>
 
+    <div id="loading" class="fullscreen-overlay">
+        <div class="sk-cube-grid full">
+            <div class="sk-cube sk-cube1"></div>
+            <div class="sk-cube sk-cube2"></div>
+            <div class="sk-cube sk-cube3"></div>
+            <div class="sk-cube sk-cube4"></div>
+            <div class="sk-cube sk-cube5"></div>
+            <div class="sk-cube sk-cube6"></div>
+            <div class="sk-cube sk-cube7"></div>
+            <div class="sk-cube sk-cube8"></div>
+            <div class="sk-cube sk-cube9"></div>
+        </div>
+    </div>
+
     <script src="lib/jquery-3.4.1.min.js" type="text/javascript"></script>
     <script src="lib/hammer.js"></script>
     <script src="lib/cornerstone.js"></script>

js/main.js

@@ -1577,3 +1577,11 @@ $("#start-exam-button").click(function (evt) {
   window.cid = parseInt($("#candidate-number").val());
   $.modal.close();
 });
+
+$(document).ajaxStart(function () {
+  $("#loading").show();
+});
+
+$(document).ajaxComplete(function () {
+  $("#loading").hide();
+});