diff --git a/notebook/static/notebook/less/renderedhtml.less b/notebook/static/notebook/less/renderedhtml.less
index b82e66a3c3..e48e5ef710 100644
--- a/notebook/static/notebook/less/renderedhtml.less
+++ b/notebook/static/notebook/less/renderedhtml.less
@@ -67,7 +67,7 @@
         table-layout: fixed;
     }
     thead {
-        border-bottom: 2px solid @rendered_html_border_color;
+        border-bottom: 1px solid @rendered_html_border_color;
         vertical-align: bottom;
     }
     tr, th, td {