diff --git a/assets/style.scss b/assets/style.scss
index 45f9c8e..c660a04 100644
--- a/assets/style.scss
+++ b/assets/style.scss
@@ -43,7 +43,7 @@ body {
 		no-repeat,
 		no-repeat;
 	background-position:
-		50% calc(50% + 1px * 0.5 * var(--scrollTop)),
+		50% calc(50% + 1px * 0.5 * var(--scrollTop, 0)),
 		50% 50%,
 		50% 50%,
 		50% 50%;