Most of kableExtra tricks will work in bookdown except those requires bootstrap. By default, rmarkdown won't load bootstrap for you on gitbook as it's not necesary. In kableExtra, I used the bootstrap 3.3.7 customization tool and made a customized css copy. You can load it by setting options(kableExtra.html.bsTable = T).
library(kableExtra) options(kableExtra.html.bsTable = T) mtcars[1:5, 1:5] %>% kable(booktabs = T) %>% kable_styling( bootstrap_options = c("striped","hover", "bordered", "condensed"), latex_options = c("striped"), full_width = F ) %>% column_spec(1, color = "red") %>% add_header_above(c(" ", "Group A" = 2, "Group B" = 3))
However, very unfortunately, as we can see, the hover part is not working and the table still looks different from a regular bootstrap table. The reason is that gitbook defines its own way to style tables and some of its rules are conflicting with the one defined in bootstrap. For css, it's like once you load something, it's impossible to really unload it. As a result, unless there are some changes in bookdown (for example, we can replace the gitbook table part with bootstrap tables), there is nothing we can do here.
Right now, it's impossible to load addition CSS through HTML dependency (due to a setting in rmarkdown). I will file an issue in rmarkdown and see if this is something that can be changed. In the mean time, to use bootstrap tables in Epub, you will have to manually load this stylesheet by putting it to a CSS file (such as "style.css") and load it in _output.yml. For example,
bookdown::epub_book: stylesheet: style.css