diff --git a/src/main/java/com/googlesource/gerrit/plugins/xdocs/public/xdocs.css b/src/main/java/com/googlesource/gerrit/plugins/xdocs/public/xdocs.css
index cf984d4..207e1b3 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/xdocs/public/xdocs.css
+++ b/src/main/java/com/googlesource/gerrit/plugins/xdocs/public/xdocs.css
@@ -5,6 +5,8 @@
 
 .xdocs-panel iframe {
   width: 100%;
+  border-width: 1px;
+  border-style: solid;
 }
 
 .xdocs-error {