added overlay feature as suggested in issue #355

build/less/boxes.less

@@ -132,7 +132,10 @@
     font-size: 12px;
     margin-bottom: 0.3em;
   }
+}
 
+.box,
+.overlay-wrapper {
   // Box overlay for LOADING STATE effect
   > .overlay,
   > .loading-img {
@@ -161,7 +164,6 @@
   .overlay.dark {
     background: rgba(0, 0, 0, 0.5);
   }
-
 }
 
 //Add clearfix to header, body and footer

dist/css/AdminLTE.css

@@ -1641,19 +1641,23 @@ a:focus {
   margin-bottom: 0.3em;
 }
 .box > .overlay,
-.box > .loading-img {
+.overlay-wrapper > .overlay,
+.box > .loading-img,
+.overlay-wrapper > .loading-img {
   position: absolute;
   top: 0;
   left: 0;
   width: 100%;
   height: 100%;
 }
-.box .overlay {
+.box .overlay,
+.overlay-wrapper .overlay {
   z-index: 50;
   background: rgba(255, 255, 255, 0.7);
   border-radius: 3px;
 }
-.box .overlay > .fa {
+.box .overlay > .fa,
+.overlay-wrapper .overlay > .fa {
   position: absolute;
   top: 50%;
   left: 50%;
@@ -1662,7 +1666,8 @@ a:focus {
   color: #000;
   font-size: 30px;
 }
-.box .overlay.dark {
+.box .overlay.dark,
+.overlay-wrapper .overlay.dark {
   background: rgba(0, 0, 0, 0.5);
 }
 .box-header:before,