diff --git a/theme/boost/scss/moodle/core.scss b/theme/boost/scss/moodle/core.scss
index 0f8a8a20dda..bc9553b83ef 100644
--- a/theme/boost/scss/moodle/core.scss
+++ b/theme/boost/scss/moodle/core.scss
@@ -1244,12 +1244,6 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
     overflow: auto;
 }
 
-.moodle-dialogue-base .moodle-dialogue-fullscreen .closebutton {
-    width: 28px;
-    height: 16px;
-    background-size: 100%;
-}
-
 .moodle-dialogue-base .moodle-dialogue-wrap {
     background-color: #fff;
     border: 1px solid #ccc;
diff --git a/theme/boost/style/moodle.css b/theme/boost/style/moodle.css
index d06c5395719..8de38ff75aa 100644
--- a/theme/boost/style/moodle.css
+++ b/theme/boost/style/moodle.css
@@ -10681,11 +10681,6 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
 .moodle-dialogue-base .moodle-dialogue-fullscreen .moodle-dialogue-content {
   overflow: auto; }
 
-.moodle-dialogue-base .moodle-dialogue-fullscreen .closebutton {
-  width: 28px;
-  height: 16px;
-  background-size: 100%; }
-
 .moodle-dialogue-base .moodle-dialogue-wrap {
   background-color: #fff;
   border: 1px solid #ccc; }
diff --git a/theme/classic/style/moodle.css b/theme/classic/style/moodle.css
index e4b4abc3990..879a0dcad3f 100644
--- a/theme/classic/style/moodle.css
+++ b/theme/classic/style/moodle.css
@@ -10886,11 +10886,6 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
 .moodle-dialogue-base .moodle-dialogue-fullscreen .moodle-dialogue-content {
   overflow: auto; }
 
-.moodle-dialogue-base .moodle-dialogue-fullscreen .closebutton {
-  width: 28px;
-  height: 16px;
-  background-size: 100%; }
-
 .moodle-dialogue-base .moodle-dialogue-wrap {
   background-color: #fff;
   border: 1px solid #ccc; }