diff --git a/theme/boost/scss/moodle/core.scss b/theme/boost/scss/moodle/core.scss
index ca671178d1c..987fed9d544 100644
--- a/theme/boost/scss/moodle/core.scss
+++ b/theme/boost/scss/moodle/core.scss
@@ -1258,12 +1258,6 @@ 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 5241ce349bf..9071fc37a5e 100644
--- a/theme/boost/style/moodle.css
+++ b/theme/boost/style/moodle.css
@@ -10694,11 +10694,6 @@ 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 0f07f2b31f5..9b59b04e7d7 100644
--- a/theme/classic/style/moodle.css
+++ b/theme/classic/style/moodle.css
@@ -10898,11 +10898,6 @@ 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; }