content/static/css: increase size of h4

The size of h4s is increased, so that functions and types are displayed
at a more readable size.

Change-Id: I48df1bcfe4d319b0a3ae78f4ab89185525d08a17
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/259624
Reviewed-by: Jamal Carvalho <jamal@golang.org>
Trust: Julie Qiu <julie@golang.org>
diff --git a/content/static/css/unit_doc.css b/content/static/css/unit_doc.css
index e066ef3..a8f1523 100644
--- a/content/static/css/unit_doc.css
+++ b/content/static/css/unit_doc.css
@@ -41,3 +41,6 @@
   height: 7.8125rem;
   width: auto;
 }
+.UnitDoc .Documentation h4 {
+  font-size: 1.375rem;
+}