diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 83c916c4b52c4db27310970c782c236a787b6892..ef81e7db0abd2bd3e208173803739eee62897c8d 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -51,7 +51,7 @@ pages:
                -o ${TARGET} ../slides/${MDFILE} \
                -V revealjs-url=https://unpkg.com/reveal.js/ \
                -V theme=${REVEAL_THEME} \
-               --include-in-header=../slides/dumux_course.css
+               --include-in-header=../slides/dumux_course_header.html
       done
     cd ..
   - mkdir public && mv build/* public && cp -r slides/img public
diff --git a/slides/dumux_course.css b/slides/dumux_course_header.html
similarity index 94%
rename from slides/dumux_course.css
rename to slides/dumux_course_header.html
index 73ef7c739aeed9e838164e09bd80ed71ef621d24..7dd8698e460f7c34b6fb8333016a1192c4c6a7a1 100644
--- a/slides/dumux_course.css
+++ b/slides/dumux_course_header.html
@@ -1,4 +1,4 @@
-<style>
+<script>
 @import url("https://fonts.googleapis.com/css?family=Nanum+Gothic");
 
 :root {
@@ -21,6 +21,7 @@
 
 .reveal pre {
     width: 100%;
+    overflow: scroll;
 }
 
 .reveal pre code {
@@ -45,5 +46,4 @@
     font-size: 1.75em;
     font-family: var(--font-family), sans-serif;
 }
-
-</style>
+</script>