Allow user to specify background colors for layouts.

Make templates work with both Remix and Next.

Switch to Tailwind for improved DX.

Use updated imports for goofy-goober.

The layout args have a separate auxiliary items shown flag for
displaying more items from left sidebar with menu layout.

Separate styles from framework implementations.

Use css-utils, which is powered by Goober, for separating HTML semantics
and styling, as compared from styled-components where semantics and
styling are defined together.