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.

Start by locating the slide deck in the repository and review the Appendix in the training manual for guidance. The issue does not identify files, specific visual problems, or objective completion criteria, so confirm the intended design scope before making changes.

索引モデルが issue の本文から書いたものです。