bookdown 0.27

• Fix fence_theorems() so that output is not ignored anymore. With previous version, when output was different than NULL, the result was written to input, ignoring output value. From now on, set input and output to the same file if you want to overwrite (thanks, @Scinawa, #1342).

• Tweak bs4_book() default CSS for better support of python chunk highlighting (thanks, @briandk, #1333).

• Fix an issue with guessing output format when no output_format is provided in render_book() for files in a rmd_subdir folder (thanks, @shivam7898, #1331).

• Fix the issue of the invisible gitbook toolbar on iPad (thanks, @mpereira-dev, #60).