Ensure that the search bar is visible when focused via anchor link

The anchor links in the skip links navigation cause the search
bar to be focused when activated, but in some cases the bar itself
is scrolled up and out of view, making it hard to interact with
after focusing.

This adds some styling to create an extra scroll margin so that
the search elements stay within view when focused using an anchor
link.

Ref sul-dlss/earthworks#1467

app/assets/stylesheets/blacklight/_search_form.scss

@@ -27,3 +27,10 @@
   border-bottom-left-radius: 0;
   display: flex;
 }
+
+// ensure that the search bar appears at the top of the page when focused using
+// anchor links, e.g. from the skip links navigation
+.search-field,
+.search-q {
+  scroll-margin: 5rem;
+}