Chapter 3. Dissecting a Theme

Drupal 8 provides us, as developers and designers, with a unique opportunity to change the appearance of the output content. We have the ability to manage the configuration from the admin user interface as well as work with the actual templates and variables that output the HTML, CSS, and JavaScript. To get a better understanding, we will take a look at dissecting a theme, as we cover the following:

• Having a proper development environment is important when working with themes, so we will take a look at the steps involved in configuring our local environment.
• Next, we will compare the similarities and differences between core default themes and custom themes while looking at how configuration has changed in Drupal 8 with the introduction of the info.yml file.
• Being able to breakdown how the metadata of the info.yml works in conjunction with general information, libraries, and regions will ensure that we have a better understanding of Drupal's theme configuration.
• The role of templates, where to find core templates, and the process of overriding templates plays a major role in theming, so we will introduce ourselves to the Twig templating system.
• Finally, we will look at the role the theme file plays in manipulating template variables and how we can use it to our advantage when working with the content.