Spray foam insulation
This page stands in for a contractor's existing website. The contractor pastes one script tag, and the instant-quote widget appears on the right (or below on a phone).
The host page uses intentionally ugly CSS (pink inputs, Comic Sans buttons). The widget renders inside shadow DOM and an iframe, so none of it leaks in.
Demo note: the price range comes from the price book saved in this browser by the app (Price book page). Submitted leads go to the app's Leads inbox in this browser. The "email to contractor" step is stubbed.