diff --git a/book/theme/custom.css b/book/theme/custom.css
index a14a003..78c80e9 100644
--- a/book/theme/custom.css
+++ b/book/theme/custom.css
@@ -206,7 +206,8 @@ strong {
 	font-family: 'Sans Bold', sans-serif;
 }
 
-.nav-chapters {
+.nav-chapters,
+.mobile-nav-chapters {
 	background-color: #fafafa !important;
 }
 
diff --git a/theme/custom.css b/theme/custom.css
index a14a003..78c80e9 100644
--- a/theme/custom.css
+++ b/theme/custom.css
@@ -206,7 +206,8 @@ strong {
 	font-family: 'Sans Bold', sans-serif;
 }
 
-.nav-chapters {
+.nav-chapters,
+.mobile-nav-chapters {
 	background-color: #fafafa !important;
 }