We use Google's Programmable Search Engine tool. When enabled, it matches your theme's brand and displays no advertising.
This is quick and easy to set up but requires us to enable it, so please contact us if you'd like to enable Website Search.
One limitation is that because the tool is powered by Google's core search technology, it is only able to search published/publicly available content. So if you have any content that only displays to logged-in users, we are unable to implement the search tool for those pages or websites.