diff --git a/theme/boost/scss/moodle/core.scss b/theme/boost/scss/moodle/core.scss
index 7707955130d..7ccda58d156 100644
--- a/theme/boost/scss/moodle/core.scss
+++ b/theme/boost/scss/moodle/core.scss
@@ -1103,6 +1103,18 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
     background-color: $gray;
 }
 
+// Prevent adding backdrops to popups in popups.
+.pagelayout-popup {
+    .moodle-dialogue-base {
+        .moodle-dialogue-lightbox {
+            background-color: transparent;
+        }
+        .moodle-dialogue {
+            box-shadow: $popover-box-shadow;
+        }
+    }
+}
+
 .moodle-dialogue-base .hidden,
 .moodle-dialogue-base .moodle-dialogue-hidden {
     display: none;
diff --git a/theme/bootstrapbase/less/moodle/core.less b/theme/bootstrapbase/less/moodle/core.less
index eeb6b2fdadc..98d7c19bfab 100644
--- a/theme/bootstrapbase/less/moodle/core.less
+++ b/theme/bootstrapbase/less/moodle/core.less
@@ -1332,6 +1332,14 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
 .moodle-dialogue-base .moodle-dialogue-lightbox {
     background-color: #aaa;
 }
+// Prevent adding backdrops to popups in popups.
+.pagelayout-popup {
+    .moodle-dialogue-base {
+        .moodle-dialogue-lightbox {
+            background-color: transparent;
+        }
+    }
+}
 .moodle-dialogue-base .hidden,
 .moodle-dialogue-base .moodle-dialogue-hidden {
     display: none;
diff --git a/theme/bootstrapbase/style/moodle.css b/theme/bootstrapbase/style/moodle.css
index 109ca2f51fb..249e0f8211b 100644
--- a/theme/bootstrapbase/style/moodle.css
+++ b/theme/bootstrapbase/style/moodle.css
@@ -3659,6 +3659,9 @@ body#page-lib-editor-tinymce-plugins-moodlemedia-preview {
 .moodle-dialogue-base .moodle-dialogue-lightbox {
   background-color: #aaa;
 }
+.pagelayout-popup .moodle-dialogue-base .moodle-dialogue-lightbox {
+  background-color: transparent;
+}
 .moodle-dialogue-base .hidden,
 .moodle-dialogue-base .moodle-dialogue-hidden {
   display: none;