diff --git a/wagtail/wagtailadmin/static_src/wagtailadmin/scss/panels/rich-text.scss b/wagtail/wagtailadmin/static_src/wagtailadmin/scss/panels/rich-text.scss
index 6cf002945..a12e86933 100644
--- a/wagtail/wagtailadmin/static_src/wagtailadmin/scss/panels/rich-text.scss
+++ b/wagtail/wagtailadmin/static_src/wagtailadmin/scss/panels/rich-text.scss
@@ -28,6 +28,7 @@
 }
 
 .hallotoolbar button{
+    /* Some of this is copied from the jQuery UI style, forcing those styles to apply to this selector. Without it, if your cursor is placed above a button while it's appearing, the CSS from jQuery UI won't immediately be applied. */
     @include border-radius(0);
     height:2.4em;
     border: 1px solid $color-grey-3;