basic divider lines for tiles

res/css/structures/_GroupGridView.scss

@@ -18,8 +18,6 @@ limitations under the License.
     display: grid;
     grid-template-columns: 1fr 1fr 1fr;
     grid-template-rows: 1fr 1fr;
-    grid-column-gap: 10px;
-    grid-row-gap: 10px;
     background-color: red;
 }
 
@@ -30,6 +28,11 @@ limitations under the License.
     content: "no room in this tile yet";
 }
 
+.mx_RoomGridView_tile {
+    border-right: 1px solid $panel-divider-color;
+    border-bottom: 1px solid $panel-divider-color;
+}
+
 .mx_RoomGridView_tile > .mx_RoomView {
     height: 100%;
 }