diff --git a/src/less/base/tree/tree.expander.less b/src/less/base/tree/tree.expander.less
index 371e39eec..76a77a655 100644
--- a/src/less/base/tree/tree.expander.less
+++ b/src/less/base/tree/tree.expander.less
@@ -13,6 +13,9 @@
 }
 
 .bi-theme-dark {
+  .bi-tree-expander-popup.line:before {
+    border-left: 1px dashed @color-bi-border-tree-expander-popup-line-theme-dark;
+  }
   .bi-tree-expander-popup.line.solid:before {
     border-left: 1px solid @color-bi-border-tree-expander-popup-line-theme-dark;
   }