Next to the app itself, it also deploys a Storybook, showcasing the app in the various states it can be in. This is perfect for quickly verifying the effect of styling changes, without having to run through countless scenarios in order to reproduce specific app states.
All this is powered by freely available open source tools. More info at my blog: https://vincenttunru.com/fearless-deployments/
To make that even easier, the pipeline also runs a visual regression test, which compares the various states of the app to reference screenshots created earlier. This prevents the inclusion of unintended changes, and allows me to view the effects of my changes at a glance.