Expose classname for extending components.

Switch to Tailwind for improved DX.

Make the more items occupy the rest of the screen's width in
left-sidebar-with-menu layout.

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.