content/static: fix sticky header margin on non-documentation pages

Fixes the margin of the sticky header on versions, licenses, imports
and imported by pages.

Change-Id: Ied69420bf5344a34a4b721e7a292831ac5e9ad33
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/306429
Trust: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>

content/static/css/unit_header.css

@@ -16,13 +16,25 @@
 }
 .UnitHeader-outer {
   background-color: var(--white);
-  min-height: 13.0625rem;
+  min-height: 6.0625rem;
   position: sticky;
-  top: -9.5rem;
+  top: -2.5rem;
   z-index: 100;
 }
+.UnitHeader-outer--main {
+  min-height: 9.5625rem;
+  top: -6rem;
+}
+.UnitHeader-outer--main.UnitHeader-outer--package {
+  min-height: 13.0625rem;
+  top: -9.5rem;
+}
 @media only screen and (min-width: 64rem) {
-  .UnitHeader-outer {
+  .UnitHeader-outer--main {
+    min-height: 6.0625rem;
+    top: -2.5rem;
+  }
+  .UnitHeader-outer--main.UnitHeader-outer--package {
     min-height: 6.0625rem;
     top: -2.5rem;
   }

content/static/html/helpers/_unit_header.tmpl

@@ -9,7 +9,9 @@
 {{define "unit_header"}}
   {{template "unit_header_breadcrumbs" .}}
   <div class="js-headerSentinel"></div>
-  <div class="UnitHeader-outer">
+  <div class="UnitHeader-outer
+      {{if .Unit.IsPackage}} UnitHeader-outer--package{{end}}
+      {{if eq .SelectedTab.Name ""}} UnitHeader-outer--main{{end}}">
     <header class="UnitHeader UnitHeader--full js-unitHeader" role="complementary"
       aria-label="{{if eq .PageType "std"}}module{{else}}{{.PageType}}{{end}} {{.Title}} information">
       <div class="Site-margin UnitHeader-inner">