diff --git a/style/mobile/components/back-top/v2/_var.less b/style/mobile/components/back-top/v2/_var.less
index 28a6b5ea45..e2f40d73ac 100644
--- a/style/mobile/components/back-top/v2/_var.less
+++ b/style/mobile/components/back-top/v2/_var.less
@@ -11,7 +11,7 @@
 @back-top-round-color: var(--td-back-top-round-color, @font-gray-1);
 @back-top-round-bg-color: var(--td-back-top-round-bg-color, @font-white-1);
 @back-top-round-border-color: var(--td-back-top-round-border-color, @component-border);
-@back-top-round-dark-border-color: var(--td-back-top-round-border-color, @font-gray-9);
+@back-top-round-dark-border-color: var(--td-back-top-round-border-color, @gray-color-9);
 @back-top-round-border-radius: var(--td-back-top-round-border-radius, @radius-circle);
 @back-top-round-dark-color: var(--td-back-top-round-dark-color, @font-white-1);
 @back-top-round-dark-bg-color: var(--td-back-top-round-dark-bg-color, @gray-color-14);