Integrations are how Spotlight exposes behavior in the Overlay. For example, the default Sentry integration enables the Errors and Traces panels.
The full content, including the tabs and panels are React components. This means you can create your own integrations and add them to the Overlay. The parts in red are for example all the parts provided by the Sentry integration.
Spotlight overlay itself really only is a slim skeleton for configured integrations. The minimal configuration of an integration has to have is and name and a version. See the integration interface for more details.