bookdownThemeEditor provides an RStudio addin that helps you easily customize the look of bookdown::gitbook.
Right now you can only get this awesome package on github.
devtools::install_github("hebrewseniorlife/bookdownThemeEditor")The only external function in this package is an RStudio Addin. It has a graphical interface, which is easy to use. ;)
Basically it helps you generate a style.css file, which you can put in your bookdown project folder. You will need to load this css by yourself by putting something like this in your _output.yml.
bookdown::gitbook:
css: style.css
Result you will get after you load style.css.
There is no difference except it's just easier to use this app. I spent some time to figure out which CSS tag needs to be modified so you don't need to. ;)