diff --git a/asciinema/theme/custom.css b/asciinema/theme/custom.css
index 6ae161d..053a72b 100644
--- a/asciinema/theme/custom.css
+++ b/asciinema/theme/custom.css
@@ -85,10 +85,11 @@ nav,
   background-color: var(--metal-bg-elevated) !important;
 }
 
-/* Override asciinema's .l-app header .navbar.bg-dark black background */
-.l-app header .navbar.bg-dark,
-.l-app header .navbar-dark.bg-dark,
-.l-app header nav.navbar.bg-dark {
+/* Override asciinema's .l-app header .navbar.bg-dark black background with maximum specificity */
+body .l-app header .navbar.bg-dark,
+body .l-app header .navbar-dark.bg-dark,
+body .l-app header nav.navbar.bg-dark,
+html body .l-app header .navbar.bg-dark {
   background-color: var(--metal-bg-elevated) !important;
 }