diff --git a/static/runestone-custom-sphinx-bootstrap.css b/static/runestone-custom-sphinx-bootstrap.css
index 9ff2904f4..e6c56e842 100644
--- a/static/runestone-custom-sphinx-bootstrap.css
+++ b/static/runestone-custom-sphinx-bootstrap.css
@@ -639,6 +639,11 @@ div.settingsbox {
     /* 1 */
 }
 
+/* hide original webwork problem when an iframe is opened */
+div.hidden-content {
+    display: none;
+}
+
 /*
  * Extends the .visuallyhidden class to allow the element
  * to be focusable when navigated to via the keyboard:
@@ -680,4 +685,4 @@ div.settingsbox {
     list-style-type: none;
     font-style: italic;
     color: blue;
-}
\ No newline at end of file
+}