Themes define the regions that are available for site administrators to place blocks in, creating a layout framework within which the components that compose a page can be placed. As a theme developer you'll need to determine what regions are necessary to accommodate your design's layout, while also ensuring it'll work with the way Drupal uses blocks to place content onto the page. Deciding what regions to create requires knowledge of how Drupal works and a clear vision of the design you're trying to achieve.

In this tutorial we'll:

Customizing the available regions in your theme is one of the first things you'll do when creating your own themes. Doing so gives you complete control over where content is displayed on the page, and the markup involved. Adding regions to a theme is a two-step process that involves editing your theme's THEMENAME.info.yml file and updating your page.html.twig file.

In this tutorial we'll:

One important aspect of theme administration is the configuration of global and theme-specific settings. In this tutorial, you will learn where theme settings are configured in Drupal's administrative interface, the difference between global and theme-specific settings, and what each global setting refers to on a base installation of Drupal with a custom theme installed.

Goal

Get a high-level overview of theme settings in Drupal.

Prerequisites

What Is a Theme?

Some, but not all, themes come with administrator-configurable settings that you can change through the UI. These might allow you to upload your own logo, choose between a couple of different pre-defined layouts, or turn features of a theme on or off. In this tutorial we'll look at where you can find these theme settings if they exist, and how to go about changing them.

Goal

Understand how to customize theme settings using the administrative UI.

An asset library is a bundle of CSS and/or JavaScript files that work together to provide a style and functionality for a specific component. They are frequently used to isolate the functionality and styling of a specific component, like the tabs displayed at the top of each node, into a reusable library. If you want to include CSS and/or JavaScript in your Drupal theme or module you'll need to declare an asset library that tells Drupal about the existence, and location, of those files.

New asset libraries can be defined by either modules or themes. In order to define a new asset library you need to create the requisite CSS and JavaScript files, and a new THEMENAME.libraries.yml, or MODULENAME.libraries.yml file that aggregates them together and provides metadata about the library itself and any dependencies.

In this tutorial we'll:

Once you've defined an asset library you'll need to tell Drupal when you want to add the CSS and JavaScript that it includes to the page. Ideally you'll do so in a way that allows Drupal to only add the corresponding assets on pages where they are needed.

Custom themes in Drupal must be configured to inherit settings, templates, and other assets from a parent theme. Which base theme you use is configurable. This allows theme developers to use a different set of markup as the starting point for their theme, organize various theme assets into a more maintainable structure, and more. All of this is made possible because of how Drupal's theme layer uses a chain of inheritance when assembling all the parts of a theme.

Drupal core comes with a few base themes: Stable, Stable 9, Classy, and Stark. Each one has a different intended use case. And all of them are useful as a reference for building your own themes.

In this tutorial we'll:

Make your theme a subtheme of a base theme, allowing it to inherit all the base theme's templates and other properties. When creating Drupal themes it is common to use the Classy theme provided with Drupal core as a base theme to jumpstart your development.

In this tutorial we'll learn how to:

This tutorial demonstrates how to locate the template file that is currently being used to render an element and override it in your own theme. This is an important skill for anyone who wants to make changes to Drupal's default HTML markup.

In this tutorial we'll:

Knowing how to inspect the variables available within a template file enables you to discover all of the dynamic content in a Twig file, not just that which is already being used.

In this tutorial, we'll learn how to use {{ dump() }}, kint(), vardumper(), and XDebug to inspect variables in a template file.

Goal

Discover and inspect variables available in any template file.

When determining which template file to use to theme an element, Drupal uses the list of theme hook suggestions to look for the best match. This allows for fine-grained control over how things appear based on dynamic state and contextual information in your application. The list of theme hook suggestions varies for each base template, so we need a way to figure out our options.

In this tutorial we'll look at:

Preprocess functions are specially-named PHP functions that allow themes and modules to modify the variables passed to a Twig template file. They are commonly used by themes to alter existing variables before they are passed to the relevant template files. For example; Changing the makeup of render array so that it renders an <ol> list instead of a <ul> list. Or appending data to the label of a node depending on custom logic.

In this tutorial we'll:

Themes and modules can alter the list of theme hook suggestions in order to add new ones, remove existing ones, or reorder the list. This powerful feature allows for the definition of custom logic in your application that can tell Drupal to use different templates based on your own unique needs. You might for example; use a different page template for authenticated users, or a custom block template for someone's birthday.

In this tutorial we'll cover:

Hooks allow modules to alter and extend the behavior of Drupal core, or another module. They are one of the various ways that code components in Drupal can communicate with one another. Using hooks a module developer can change how core or another module works -- without changing the existing code. As a Drupal developer, understanding how to implement and invoke hooks is essential.

In this tutorial we'll:

Hooks allow module developers to execute custom code at key moments during Drupal's request processing life cycle. They can be used to react to actions or conditions, alter forms and existing configuration, and extend Drupal in various ways. Knowing how to implement a hook is an essential skill for any Drupal developer.

In this tutorial we'll walk through the process of locating the documentation for a specific hook, and then implementing it. All hooks are implemented in the same way, so once you know how to implement one, you'll be able to implement any.

The Responsive Image module provides a process for transforming images uploaded through image fields into responsive images. This is accomplished through the configuration of responsive image styles. The configuration form for adding and editing responsive image styles is quite extensive. In this tutorial, we'll go through this form and learn what each option entails. By the end of this lesson, you should have a good understanding of the various options in the responsive image style configuration form.

You might already be familiar with image styles in Drupal. Image styles are a popular and commonly used feature of Drupal because they enable your site's content creators to upload an image once, but have it displayed at various sizes and resolutions depending on its context. Image styles are configured and then applied to an image field's display settings, whether using view modes, Views field settings, or other contexts.

In this tutorial, we're going to add a responsive image style to an image field on the Article content type. This will add the srcset and sizes attributes to the output <img> element, providing media conditions, width descriptors, and a set of image sources for the browser to choose from, depending on the user device's viewport size.

Drupal comes with all of its caching features enabled by default. This improves response time, but can be frustrating for themers as it makes it harder to preview the changes you make to template files.

In this tutorial we'll look at:

• Why these features are enabled by default
• How the theme layer leverages Drupal's caches
• Why you should learn to disable them when doing development

Goal

Understand which performance-related features in Drupal are turned on by default and how this can impact theme and front-end developers.