content/static/css: make pages more printer-friendly

Fixes golang/go#43238

Change-Id: Ice5386fc7e0293fbfa831069ae9e23526d5893e2
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/278873
Run-TryBot: Baokun Lee <bk@golangcn.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
Trust: Julie Qiu <julie@golang.org>
diff --git a/content/static/css/sidenav.css b/content/static/css/sidenav.css
index 77a14e7..2b1deda 100644
--- a/content/static/css/sidenav.css
+++ b/content/static/css/sidenav.css
@@ -30,6 +30,11 @@
   transition: box-shadow 0.2s linear;
   z-index: 4;
 }
+@media print {
+  .DocNavMobile {
+    display: none;
+  }
+}
 .DocNavMobile--withShadow {
   box-shadow: 0 0.1875rem 0.1875rem rgba(0, 0, 0, 0.2);
 }
diff --git a/content/static/css/unit_fixed_header.css b/content/static/css/unit_fixed_header.css
index d590a1c..093e82b 100644
--- a/content/static/css/unit_fixed_header.css
+++ b/content/static/css/unit_fixed_header.css
@@ -16,6 +16,11 @@
   width: 100%;
   z-index: 1000;
 }
+@media print {
+  .UnitFixedHeader {
+    display: none;
+  }
+}
 .UnitFixedHeader--visible {
   transform: unset;
 }