diff --git a/grade/report/grader/styles.css b/grade/report/grader/styles.css
index 977e305e1e4..e5c83800595 100644
--- a/grade/report/grader/styles.css
+++ b/grade/report/grader/styles.css
@@ -586,7 +586,7 @@ background-color:#f3ead8;
 
 .path-grade-report-grader .grade_icons { margin-bottom: .3em;}
 
-.path-grade-report-grader .yui-overlay {
+.path-grade-report-grader .yui3-overlay {
     background-color: #FFEE69;
     border-color: #D4C237 #A6982B #A6982B;
     border-style: solid;
@@ -596,15 +596,15 @@ background-color:#f3ead8;
     font-size: 0.7em;
 }
 
-.path-grade-report-grader .yui-overlay .fullname {
+.path-grade-report-grader .yui3-overlay .fullname {
     color: #5F3E00;
     font-weight: bold;
 }
-.path-grade-report-grader .yui-overlay .itemname {
+.path-grade-report-grader .yui3-overlay .itemname {
     color: #194F3E;
     font-weight: bold;
 }
-.path-grade-report-grader .yui-overlay .feedback {
+.path-grade-report-grader .yui3-overlay .feedback {
     color: #5F595E;
 }
 /* table#user-grades td */
@@ -613,7 +613,7 @@ background-color:#f3ead8;
   text-align: left;
 }
 
-.path-grade-report-grader .yui-overlay a.container-close {
+.path-grade-report-grader .yui3-overlay a.container-close {
   margin-top: -3px;
 }