diff --git a/scripts/gh-book/gh-book.less b/scripts/gh-book/gh-book.less
index 60d0dd1a..8ab0a8a1 100755
--- a/scripts/gh-book/gh-book.less
+++ b/scripts/gh-book/gh-book.less
@@ -187,6 +187,12 @@ nav#workspace-sidebar-toc{
   .icon-math *:before {
     content: "";
   }
+  .icon-undo:before {
+    content: "\e007";
+  }
+  .icon-redo:before {
+    content: "\e00a";
+  }
 
 }