Fix orange outline on global site search

The global header was recently updated to use the search component
instead of a hard coded search field.

This resulted in an issue where the input outline is now orange due to
more specific styles from govuk_template conflicting with the search
component styles.

This updates the component styles to be more specific in order to
override the CSS from govuk_template.

app/assets/stylesheets/govuk_publishing_components/components/_search.scss

@@ -34,7 +34,8 @@ $large-input-size: 50px;
   }
 }
 
-.gem-c-search__input[type="search"] { // overly specific to prevent some overrides from outside
+.gem-c-search__input[type="search"],
+#global-header .gem-c-search__input[type="search"] { // overly specific to prevent some overrides from outside
   @include govuk-font($size: 19, $line-height: (28 / 19));
 
   padding: 6px;