diff --git a/phpBB/styles/prosilver/theme/content.css b/phpBB/styles/prosilver/theme/content.css
index 2296a15224..592269a0b3 100644
--- a/phpBB/styles/prosilver/theme/content.css
+++ b/phpBB/styles/prosilver/theme/content.css
@@ -689,6 +689,8 @@ dl.thumbnail dt a:hover img {
 }
 
 .c-file-audio-source {
+
+	/** placeholder */
 }
 
 .c-file-video-controls {
@@ -696,6 +698,8 @@ dl.thumbnail dt a:hover img {
 }
 
 .c-file-video-source {
+
+	/** placeholder */
 }
 
 /* Post poll styles