Inline CSS in Built Jekyll Project.

inline_css.rb

Dir[File.join('_site', '**', '*')].reject { |p| File.directory? p }
  .reject { |filename| !filename[/\.html/] }
  .each do |file|
    main_css = File.read('_site/css/main.css')
    old_contents = File.read(file)
    new_contents = old_contents.gsub(
      "<link href='css/main.css' rel='stylesheet'>",
      "<style>#{main_css}</style>"
    )
    File.open(file, 'w') { |newfile| newfile.write(new_contents) }
  end