Topo2 - Show 'No Devices Connected' message
JIRA Tasks; ONOS-6290

Change-Id: Ibe70452da14c0c2ebb01d3ece7328f1b7936c625
diff --git a/web/gui/src/main/webapp/app/view/topo2/topo2.css b/web/gui/src/main/webapp/app/view/topo2/topo2.css
index 81c14d5..b4ffd80 100644
--- a/web/gui/src/main/webapp/app/view/topo2/topo2.css
+++ b/web/gui/src/main/webapp/app/view/topo2/topo2.css
@@ -32,6 +32,16 @@
 }
 
 
+/* --- "No Devices" Layer --- */
+
+#ov-topo2 svg #topo2-noDevsLayer {
+    visibility: hidden;
+}
+
+#ov-topo2 svg #topo2-noDevsLayer text {
+    font-size: 60pt;
+    font-style: italic;
+}
 
 #breadcrumbs {
     font-size: 13px;