diff --git a/lectures/custom.scss b/lectures/custom.scss
index 31184f94364a323c47038e59f9a522abdf33e52b..0ed79eb9347de7853daa5368a703a4d84b8ae743 100644
--- a/lectures/custom.scss
+++ b/lectures/custom.scss
@@ -102,6 +102,10 @@ kbd, .kbd {
   background-position: right top; 
 }
 
+.reveal div.sourceCode {
+    background-color: transparent;
+}
+
 .reveal .special.slide-background {
   background-color: var(--dark-bg-color);
 }