diff --git a/index.css b/index.css
index ed81773f..c8d5efb0 100644
--- a/index.css
+++ b/index.css
@@ -50,6 +50,7 @@ iframe {
   mask-mode: alpha;
   mask-clip: no-clip;
   fill-rule: evenodd;
+  user-select: none;
 }
 
 #canvas {