The tab-bar affordance can use shadow-dom to establish a styleable tab-bar and panels. The required parts can be exposed for styling with consistent pseudo-elements.

The accordion-like collapse affordance also uses shadow-dom to establish summary-details like behavior for each section, with an option to make the toggle-states exclusive-collapse.

The fallback state is simply structured HTML, without any show/hide affordances. This does not require any special styling.