overwrite default bootstrap styling

I'd like us to steer away of the default bootstrap look, and steer toward a look that fits in with Rust's aesthetic. We should look around at rust-affiliated websites and take inspiration from their designs.

Sites to check out:
- [rust-lang.org](https://www.rust-lang.org/)
- [docs.rs](https://docs.rs/)
- [the rust users forum](https://users.rust-lang.org/)

See [this video](https://www.youtube.com/watch?v=6Ovw43Dkp44) for how to setup the bootstrap theme customization.

Review the Bootstrap theme-customization video and compare the listed Rust-affiliated sites for visual direction. Identify where the current default Bootstrap styling is applied, then define a consistent Rust-inspired appearance across the interface; done means the default Bootstrap look has been replaced with an agreed design.

Written by the indexing model from the issue text.