diff --git a/web/gui/src/main/webapp/topo2.css b/web/gui/src/main/webapp/topo2.css
index 2e058c1..88fcd94 100644
--- a/web/gui/src/main/webapp/topo2.css
+++ b/web/gui/src/main/webapp/topo2.css
@@ -20,3 +20,7 @@
  @author Simon Hunt
  */
 
+svg #topo-bg {
+    opacity: 0.5;
+}
+