Restyle the Slides

## Do you have an eye for design?
Help us improve the look of the slide deck.
If you need help, check out the Appendix in the training manual.

The issue does not name a slide-deck file, test, or entry point; locate the deck in the repository and read the Appendix in the training manual for context. Define the visual improvements before starting, then confirm the revised slides have a more consistent and polished appearance.

Written by the indexing model from the issue text.