diff --git a/B03_FileInput/B03_FileInput_UI_Style.css b/B03_FileInput/B03_FileInput_UI_Style.css
index 5c9f6146..b0e1e9ef 100644
--- a/B03_FileInput/B03_FileInput_UI_Style.css
+++ b/B03_FileInput/B03_FileInput_UI_Style.css
@@ -614,8 +614,9 @@
 }
 
 .b03-file__preview-extent {
-  fill: color-mix(in srgb, var(--color-border, #9aa) 35%, transparent);
+  fill: color-mix(in srgb, var(--color-border, #9aa) 12%, transparent);
   stroke: var(--color-border, #9aa);
+  stroke-dasharray: 4 3;
   stroke-width: 1;
 }