Add grid feature to osd preview

src/css/dark-theme.css

@@ -501,6 +501,11 @@ progress[value]::-webkit-progress-bar {
     background-size: cover;
 }
 
+.tab-osd .preview:active {
+    background: linear-gradient(rgba(0, 0, 0, 0.2), rgba(0, 0, 0, 0.2)), url(../../images/osd-bg-1-grid.png), url(../../images/osd-bg-1.jpg);
+    background-size: cover;
+}
+
 /* these two items replace the look of the checkboxes in only CSS */
 .tab-osd input[type='checkbox']:after {
     line-height: 1.5em;

src/css/tabs/osd.css

@@ -454,7 +454,7 @@ button {
   float: left; 
   position: sticky;
   top: 0;
-  margin-left: calc((100% - 362px) / 2);
+  margin-left: calc((100% - 360px) / 3);
 
 
 /* please don't copy the generic background image from another project
@@ -466,6 +466,11 @@ button {
   border-bottom-right-radius: 3px;
 }
 
+.tab-osd .preview:active {
+  background: url(../../images/osd-bg-1-grid.png), url(../../images/osd-bg-1.jpg);
+  background-size: cover;
+}
+
 .tab-osd .alarms label {
   display: block;
   width:100%;