bookdownThemeEditor
bookdownThemeEditor provides an RStudio addin that helps you easily customize the look of bookdown::gitbook.
Installation
Right now you can only get this awesome package on github.
devtools::install_github("hebrewseniorlife/bookdownThemeEditor")How to use
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.
What's the difference between using this app and creating my own stylesheet?
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. ;)

