The quick search will use the No Results Found configurations you define within the Klevu Merchant Centre, allowing you to show specific messages for certain keywords. You can also use Klevu JavaScript Library to override the templates for no results found. As for Search Results and Category pages, these preserve your native theme and as a result must be customised within your Salesforce Theme. If you want Klevu to have more control over this, you may consider using the JavaScript powered Klevu Theme for your Search Results and Category pages.