diff --git a/src/librustdoc/html/static/css/rustdoc.css b/src/librustdoc/html/static/css/rustdoc.css
index 025157713498e..aecc9aa879a69 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 */
@@ -652,7 +652,7 @@ h2.location a {
 }
 
 .top-doc .docblock h2 { font-size: 1.375rem; }
-.top-doc .docblock h3 { font-size: 1.25; }
+.top-doc .docblock h3 { font-size: 1.25rem; }
 .top-doc .docblock h4,
 .top-doc .docblock h5 {
 	font-size: 1.125rem;
diff --git a/src/librustdoc/html/static/css/themes/dark.css b/src/librustdoc/html/static/css/themes/dark.css
index 62d9eaa02e6a7..a550eb1c130af 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;
 }
diff --git a/src/test/rustdoc-gui/docblock-details.goml b/src/test/rustdoc-gui/docblock-details.goml
index 2edbf1e4e2d8c..f6287ade2f295 100644
--- a/src/test/rustdoc-gui/docblock-details.goml
+++ b/src/test/rustdoc-gui/docblock-details.goml
@@ -9,12 +9,12 @@ reload:
 assert-text: (".top-doc .docblock > h3", "Hello")
 assert-css: (
     ".top-doc .docblock > h3",
-    {"border-bottom": "1px solid rgb(221, 221, 221)"},
+    {"border-bottom": "1px solid rgb(210, 210, 210)"},
 )
 // We now check that the `<summary>` doesn't have a bottom border and has the correct display.
 assert-css: (
     ".top-doc .docblock summary h4",
-    {"border-bottom": "0px none rgb(221, 221, 221)"},
+    {"border-bottom": "0px none rgb(210, 210, 210)"},
 )
 // This allows to ensure that summary is on one line only!
 assert-property: (".top-doc .docblock summary h4", {"offsetHeight": "33"})
diff --git a/src/test/rustdoc-gui/headings.goml b/src/test/rustdoc-gui/headings.goml
index cc3dd61e99a7a..8c2c3df1588f5 100644
--- a/src/test/rustdoc-gui/headings.goml
+++ b/src/test/rustdoc-gui/headings.goml
@@ -150,15 +150,109 @@ assert-css: ("h2#top-doc-prose-title", {"border-bottom-width": "1px"})
 assert-css: ("h3#top-doc-prose-sub-heading", {"font-size": "20px"})
 assert-css: ("h3#top-doc-prose-sub-heading", {"border-bottom-width": "1px"})
 
-goto: file://|DOC_PATH|/staged_api/struct.Foo.html
+// Checking colors now.
 show-text: true
 local-storage: {"rustdoc-theme": "light", "rustdoc-use-system-theme": "false"}
+goto: file://|DOC_PATH|/test_docs/struct.HeavilyDocumentedStruct.html
+assert-css: (
+    ".top-doc .docblock h2",
+    {"color": "rgb(0, 0, 0)", "border-bottom": "1px solid rgb(221, 221, 221)"},
+)
+assert-css: (
+    ".top-doc .docblock h3",
+    {"color": "rgb(0, 0, 0)", "border-bottom": "1px solid rgb(221, 221, 221)"},
+)
+assert-css: (
+    ".top-doc .docblock h4",
+    {"color": "rgb(0, 0, 0)", "border-bottom": "1px solid rgb(221, 221, 221)"},
+)
+assert-css: (
+    ".top-doc .docblock h5",
+    {"color": "rgb(0, 0, 0)", "border-bottom": "0px none rgb(221, 221, 221)"},
+)
+assert-css: (
+    "#implementations-list .docblock h4",
+    {"color": "rgb(0, 0, 0)", "border-bottom": "0px none rgb(221, 221, 221)"},
+)
+assert-css: (
+    "#implementations-list .docblock h5",
+    {"color": "rgb(0, 0, 0)", "border-bottom": "0px none rgb(221, 221, 221)"},
+)
+assert-css: (
+    "#implementations-list .docblock h6",
+    {"color": "rgb(0, 0, 0)", "border-bottom": "0px none rgb(221, 221, 221)"},
+)
+
+local-storage: {"rustdoc-theme": "dark"}
+reload:
+assert-css: (
+    ".top-doc .docblock h2",
+    {"color": "rgb(221, 221, 221)", "border-bottom": "1px solid rgb(210, 210, 210)"},
+)
+assert-css: (
+    ".top-doc .docblock h3",
+    {"color": "rgb(221, 221, 221)", "border-bottom": "1px solid rgb(210, 210, 210)"},
+)
+assert-css: (
+    ".top-doc .docblock h4",
+    {"color": "rgb(221, 221, 221)", "border-bottom": "1px solid rgb(210, 210, 210)"},
+)
+assert-css: (
+    ".top-doc .docblock h5",
+    {"color": "rgb(221, 221, 221)", "border-bottom": "0px none rgb(210, 210, 210)"},
+)
+assert-css: (
+    "#implementations-list .docblock h4",
+    {"color": "rgb(221, 221, 221)", "border-bottom": "0px none rgb(210, 210, 210)"},
+)
+assert-css: (
+    "#implementations-list .docblock h5",
+    {"color": "rgb(221, 221, 221)", "border-bottom": "0px none rgb(210, 210, 210)"},
+)
+assert-css: (
+    "#implementations-list .docblock h6",
+    {"color": "rgb(221, 221, 221)", "border-bottom": "0px none rgb(210, 210, 210)"},
+)
+
+local-storage: {"rustdoc-theme": "ayu"}
+reload:
+assert-css: (
+    ".top-doc .docblock h2",
+    {"color": "rgb(255, 255, 255)", "border-bottom": "1px solid rgb(92, 103, 115)"},
+)
+assert-css: (
+    ".top-doc .docblock h2",
+    {"color": "rgb(255, 255, 255)", "border-bottom": "1px solid rgb(92, 103, 115)"},
+)
+assert-css: (
+    ".top-doc .docblock h4",
+    {"color": "rgb(255, 255, 255)", "border-bottom": "1px solid rgb(92, 103, 115)"},
+)
+assert-css: (
+    ".top-doc .docblock h5",
+    {"color": "rgb(197, 197, 197)", "border-bottom": "0px none rgb(92, 103, 115)"},
+)
+assert-css: (
+    "#implementations-list .docblock h4",
+    {"color": "rgb(255, 255, 255)", "border-bottom": "0px none rgb(92, 103, 115)"},
+)
+assert-css: (
+    "#implementations-list .docblock h5",
+    {"color": "rgb(197, 197, 197)", "border-bottom": "0px none rgb(92, 103, 115)"},
+)
+assert-css: (
+    "#implementations-list .docblock h6",
+    {"color": "rgb(197, 197, 197)", "border-bottom": "0px none rgb(92, 103, 115)"},
+)
+
+local-storage: {"rustdoc-theme": "light"}
+goto: file://|DOC_PATH|/staged_api/struct.Foo.html
 assert-css: (".since", {"color": "rgb(128, 128, 128)"})
 
-local-storage: {"rustdoc-theme": "dark", "rustdoc-use-system-theme": "false"}
+local-storage: {"rustdoc-theme": "dark"}
 reload:
 assert-css: (".since", {"color": "rgb(128, 128, 128)"})
 
-local-storage: {"rustdoc-theme": "ayu", "rustdoc-use-system-theme": "false"}
+local-storage: {"rustdoc-theme": "ayu"}
 reload:
 assert-css: (".since", {"color": "rgb(128, 128, 128)"})
diff --git a/src/test/rustdoc-gui/src/test_docs/lib.rs b/src/test/rustdoc-gui/src/test_docs/lib.rs
index aa2f78289bea2..1b26aaecb5ef3 100644
--- a/src/test/rustdoc-gui/src/test_docs/lib.rs
+++ b/src/test/rustdoc-gui/src/test_docs/lib.rs
@@ -146,6 +146,10 @@ pub use crate::repro as repro2;
 /// ### Top-doc Prose sub-sub-heading
 ///
 /// Text below sub-sub-heading
+///
+/// #### You know the drill.
+///
+/// More text.
 pub struct HeavilyDocumentedStruct {
     /// # Title for field
     /// ## Sub-heading for field