diff --git a/src/editor/sandbox/srcdoc.html b/src/editor/sandbox/srcdoc.html
index 3dc3d807..e4389184 100644
--- a/src/editor/sandbox/srcdoc.html
+++ b/src/editor/sandbox/srcdoc.html
@@ -16,6 +16,10 @@
         position: relative;
         height: 100vh;
         overflow: hidden;
+        /* keep content centered on resize: */
+        display:flex; 
+        justify-content:center; 
+        align-items:center;	
       }
       .ec-debug-dirty-rect {
         background-color: rgba(255, 0, 0, 0.2) !important;