When there’s an update, theme developers push the update to RubyGems. Gem-based themes make it easier for theme developers to make updates available to anyone who has the theme gem. The Gemfile and Gemfile.lock files are used by Bundler to keep track of the required gems and gem versions you need to build your Jekyll site. In the case of Minima, you see only the following files in your Jekyll site directory: Yet all of the necessary directories will be read and processed during Jekyll’s build process. With gem-based themes, some of the site’s directories (such as the assets, _data, _layouts, _includes, and _sass directories) are stored in the theme’s gem, hidden from your immediate view. When you create a new Jekyll site (by running the jekyll new command), Jekyll installs a site that uses a gem-based theme called Minima. You can find and preview themes on different galleries:

Jekyll themes specify plugins and package up assets, layouts, includes, and stylesheets in a way that can be overridden by your site’s content. Jekyll has an extensive theme system that allows you to leverage community-maintained templates and styles to customize your site’s presentation.

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