I recently created individual Sass modules for each of the WordPress Twenty Sixteen style.css stylesheet numbered and annotated sections. Additionally, the fonts and colors have been converted into Sass variables. All of this makes customizing this theme easier.
May 25, 2018 – Sass has been updated for the Twenty Sixteen theme version 1.5 which comes bundled with WordPress version 4.9.6 released on May, 17, 2018.
There is also a gulpfile.js included with a task for compiling the .scss files into a new style.css. This task uses cssnano and the workflow described in this post, Sass Workflow Using cssnano and Autoprefixer.
Install the files into the /wp-content/themes/twentysixteen folder.
To recompile the Twenty Sixteen stylesheet style.css from the scss files, first run npm install to get the dependencies.
# installs dependencies npm install
Then run the gulp task that will compile them
# compile into styleheet gulp css