internal/godoc: make doc overview an h3 heading

The overview heading is downgraded to an h3 with the
addition of the documentation header.

Change-Id: I1c06e3146f42ab3e7eeca3b30e03276eac30be77
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/259625
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>
diff --git a/internal/godoc/dochtml/template_body.go b/internal/godoc/dochtml/template_body.go
index b3512b7..fb1b545 100644
--- a/internal/godoc/dochtml/template_body.go
+++ b/internal/godoc/dochtml/template_body.go
@@ -9,7 +9,7 @@
 ` + IdentifierBodyStart + ` {{/* Documentation content container */}}
 {{- if or .Doc (index .Examples.Map "") -}}
 	<section class="Documentation-overview">
-		<h2 tabindex="-1" id="pkg-overview" class="Documentation-overviewHeader">Overview <a href="#pkg-overview">¶</a></h2>{{"\n\n" -}}
+		<h3 tabindex="-1" id="pkg-overview" class="Documentation-overviewHeader">Overview <a href="#pkg-overview">¶</a></h3>{{"\n\n" -}}
 		{{render_doc .Doc}}{{"\n" -}}
 		{{- template "example" (index .Examples.Map "") -}}
 	</section>
diff --git a/internal/godoc/testdata_test.go b/internal/godoc/testdata_test.go
index 71df7eb..1bdcec5 100644
--- a/internal/godoc/testdata_test.go
+++ b/internal/godoc/testdata_test.go
@@ -58,7 +58,7 @@
 
 const quoteBody = `<div class="Documentation-content js-docContent">
    <section class="Documentation-overview">
-      <h2 tabindex="-1" id="pkg-overview" class="Documentation-overviewHeader">Overview <a href="#pkg-overview">¶</a></h2>
+      <h3 tabindex="-1" id="pkg-overview" class="Documentation-overviewHeader">Overview <a href="#pkg-overview">¶</a></h3>
       <p>Package quote collects pithy sayings.</p>
    </section>
    <section class="Documentation-index">