content/static: update header items to explicitly set margins

li items are given a top margin on some pages (release notes being
a notable example). Explicitly set all margin values to ensure
no top margin is added.

Change-Id: I4fec8130409b916cd3b10b53bfc8863c8235d28f
Reviewed-on: https://go-review.googlesource.com/c/website/+/180759
Reviewed-by: Katie Hockman <katie@golang.org>
diff --git a/content/static/style.css b/content/static/style.css
index fd45788..072ecd9 100644
--- a/content/static/style.css
+++ b/content/static/style.css
@@ -292,7 +292,7 @@
   display: inline-flex;
 }
 .Header-menuItem:not(:last-of-type) {
-  margin-bottom: 1rem;
+  margin: 0 0 1rem 0;
 }
 .Header-menuItem,
 .Header-menuItem a:link,
@@ -368,8 +368,7 @@
     width: auto;
   }
   .Header-menuItem:not(:last-of-type) {
-    margin-bottom: 0;
-    margin-right: 3rem;
+    margin: 0 3rem 0 0;
   }
   .Header-menuItem a:hover,
   .Header-menuItem a:focus {