Switch to bootstrap 4

[hadley]

• Needed for greater consistency with future releases of shiny, rmarkdown, bookdown etc.
• Probably needs to be opt-in (or definitely needs to be opt-out)
• Use bootstrap lib
• Provide a few customisation parameters (e.g. key colours + font)

[hadley]

Start from template in bookdown::bs4_book()

[jeroen]

Also note bootstrap 5 is getting close to a release: http://getbootstrap.com/ . I think this is a relatively small updated from v4, no major changes in the grid layout. https://getbootstrap.com/docs/5.0/migration/

[hadley]

I skimmed a few articles about differences between v4 and v5, and I think this is the best summary: https://designmodo.com/bootstrap-5/

[amirmasoudabdol]

I would be interested in looking into this. I started my project by adapting bootstrap 4, and considered 5 at some point too, but decided to wait for pkgdown and see how you guys are going to more forward.

In terms of compatibility, bootstrap 4 is very much compatible with 3, the only real issue is the navigation bar which needs to be rewritten. Other than that, in my prototypes, I haven't noticed anything else being broken. I think the jump from 3 to 5 is going to be more challenging, but not terribly difficult.

I might start playing around with bootstrap 5 a bit more, as I'm somewhat warmed up! 😅