diff --git a/src/librustdoc/html/static/css/rustdoc.css b/src/librustdoc/html/static/css/rustdoc.css
index 68f8de15ba2..0b9a16c5734 100644
--- a/src/librustdoc/html/static/css/rustdoc.css
+++ b/src/librustdoc/html/static/css/rustdoc.css
@@ -167,7 +167,7 @@ h2, h3, h4 {
 h2,
 .top-doc .docblock > h3,
 .top-doc .docblock > h4 {
-	border-bottom: 1px solid;
+	border-bottom: 1px solid var(--headings-border-bottom-color);
 }
 h3.code-header {
 	font-size: 1.125rem; /* 18px */
diff --git a/src/librustdoc/html/static/css/themes/dark.css b/src/librustdoc/html/static/css/themes/dark.css
index 8e753f57682..1ded3730e84 100644
--- a/src/librustdoc/html/static/css/themes/dark.css
+++ b/src/librustdoc/html/static/css/themes/dark.css
@@ -42,10 +42,6 @@ input:focus + .slider {
 	background-color: #0a042f !important;
 }
 
-.docblock h1, .docblock h2, .docblock h3, .docblock h4, .docblock h5, .docblock h6 {
-	border-bottom-color: #DDD;
-}
-
 .docblock table td, .docblock table th {
 	border-color: #ddd;
 }