Make demo site responsive

[kellyi]

Overview

The demo site really expedites testing PRs, but it's not currently set up to be responsive so I've routinely needed to set up the Parcel Viewer to import a branch from here which includes the cibuild dist output. Subsequently I accidentally merged the output artifacts outside of a git flow release:

668d088

We should adjust the Netlify demo site to make it responsive so that we can easily demo & test mobile changes on staging.

Describe the solution you'd like

Adjust the Netlify demo site to make it responsive so that we can easily demo & test mobile changes on staging.