As a theme developer you can extend an existing asset library to include custom CSS and/or JavaScript from your theme. This is useful when you want to add styles or behaviors to components provided by Drupal core or another module.

Sometimes there are CSS or JavaScript asset libraries attached to the page by Drupal core, a contributed module, or another theme, that do something you don't like, and you want to change it or even exclude it all together. There are a couple of different ways that themes can override, alter, or extend, an existing asset library in order to modify the CSS and JavaScript that get attached the page by other code belonging to another theme or module.

In this tutorial we'll learn how to:

• Extend an existing asset library using libraries-extend, so that our custom CSS and JavaScript is included whenever that library is used.
• Override an existing asset library using libraries-override, to alter the definition of the library, and replace or exclude individual assets (or the entire library).

By the end of this tutorial you should be able to use your custom theme to override, extend, or alter any of the asset libraries added to the page by another theme or module.

There’s no one-size-fits-all path to upgrade from Drupal 9 to Drupal 10, but there is a set of common tasks that everyone will need to complete.

In this tutorial we’ll:

• Explain the differences between Drupal 9 and Drupal 10 that affect the upgrade path.
• Walk through the high-level steps required to upgrade from Drupal 9 to Drupal 10.
• Provide resources to help you create an upgrade checklist and start checking items off the list.

By the end of this tutorial you should be able to explain the major differences between Drupal 9 and 10, audit your existing Drupal 9 projects for Drupal 10 readiness, estimate the level of effort involved, and start the process of upgrading.

In Drupal's Appearance UI, all themes get a theme settings form. As a theme developer, you can customize the theme settings form, enabling site administrators to have more control over the appearance of the theme.

In this tutorial, we'll show you how to add admin-configurable settings to your theme. In the process of doing this, we'll use a variety of theme and module development skills and assume you have some familiarity with using Drupal's Form API, Configuration API, and theme system (see Prerequisites).

By the end of this tutorial, you will be able to provide custom theme settings that an administrator can use to modify the appearance of the theme.

If you want to create a link to a internal page in a Twig template--and there's not already a variable in the template that contains the URL you want to link to--you'll need to determine the route of the thing you want to link to and then use the Twig url() or path() functions to generate appropriate URLs. In most cases when you want to create a link to an entity that is being output by the current template there's an existing helper variable to use. For example, in a node.html.twig template file there's a {{ url }} variable that points to the current node. For other scenarios, like hard-coding a link to the /about page, you'll need to do a little more work.

In this tutorial we'll:

• Use the Twig url() and path() functions to create full URLs for navigation

By the end of this tutorial you should be able to create links to any internal page via Twig.

Why use Migrate Upgrade and Migrate Plus? The short answer is: because it'll save you from having to type out a bunch of YAML by scaffolding a migration for you.

The contributed Migrate Plus and Migrate Upgrade modules are commonly used to aid in the process of performing a Drupal-to-Drupal migration. The combination of the two makes it easier to customize the configuration of individual migrations on a per-project basis by allowing you to edit each individual migrations configuration using the same mechanics that you would to write a custom migration.

It's not the only approach to making these changes, but for many people (including us), it's the most efficient way.

In this tutorial we'll:

• Get a more in-depth look at the role of the Migrate Plus and Migrate Upgrade modules
• Discuss the use cases for using them as part of a Drupal-to-Drupal migration

By the end of this tutorial you should be able to explain what both the Migrate Plus and Migrate Upgrade modules are used for.

When working on configuration in a module, whether as part of a migration that uses Migrate Plus configuration entities, or while developing custom configuration entities, you'll often need to re-import the configuration stored in the .yml files of the modules config/install/ or config/optional/ directories. This is tricky though, because Drupal only reads in those default configuration settings when the module is first enabled. So any changes you make to those files after the module has been installed will not be reflected without these workarounds.

Knowing how to do this can improve the developer experience of adding (or debugging) the default configuration that's provided with a module. Or for anyone using Migrate Plus configuration entities as part of a migration.

In this tutorial we'll:

• Learn about the Configuration Development module
• Look at how you can use Drush to perform a partial configuration import
• Write an implementation of hook_uninstall() to remove a module's configuration when it's uninstalled

By the end of this tutorial you should be able to re-import the configuration provided by a module without having to uninstall and then reinstall the module.

Field formatters are responsible for taking the data stored by a field and transforming it into what a vistor sees. We can define new field formatters to output data for new field types or to provide alternative formatting options for existing field types. Creating a field formatter plugin is a common task for Drupal developers.

In this tutorial we'll:

• Define a new background color field formatter that uses the string stored by our field_example_rgb field type as the background color of the output.
• Make it possible for site builders to toggle on or off a feature that automatically adjusts the foreground text color of the output.

By the end of this tutorial you should be able to define a new custom field formatter plugin with settings that a site administrator can configure.

Drush, aka The Drupal Shell, is a command line utility and UNIX scripting interface for Drupal. It allows access to common Drupal features and tasks via the command line. It can help speed up common tasks for Drupal site builders, developers, and DevOps teams. Among other things, it makes it easier to integrate Drupal into CI/CD workflows.

In this tutorial we'll:

• Learn what Drush is and what can be done with Drush
• Install Drush
• Find a list of Drush commands
• Learn how to execute commands

By the end of this tutorial, you'll understand how to install and use Drush with your Drupal projects, navigate the list of its commands and run them. This is intended as an overview. Other tutorials will provide more detail about common commands and use-cases.

Every Drupal site consists of many Drupal projects like modules and themes. Drush comes with a group of commands that aid in managing projects from the command line. These commands can check which modules are present in a site's codebase, report their security status, enable modules, and display metadata for modules and themes. All of these commands start with the pm prefix, and are part of the project manager group.

Common use cases for the project manager commands include: quickly enabling/disabling modules via the CLI rather than performing numerous clicks in the UI, and as part of CI/CD process that lists (or maybe even automates) security updates.

In this tutorial we'll:

• List the available pm commands
• Enable a module with Drush
• Uninstall a module with Drush
• Use Drush to check for security updates for modules, themes and PHP packages

By the end of this tutorial you'll have an understanding of the project manager commands that come with Drush, how to use them, and how to speed up common workflows and maintenance tasks.

Administration and maintenance of Drupal websites consists of many tasks that can both be performed via the command line, and automated, with Drush. Using Drush's site and environment administration commands you can run database updates, check an environment's status, clear (rebuild) the cache, perform Cron-related operations, and manage users. These tasks are repetitive, often require many steps in the UI, and may be tedious in the long run. Learning to execute them with Drush can save you time and allows for more automation of common tasks.

In this tutorial we'll:

• Use Drush to check a site's status
• Learn how to perform database updates with Drush
• Clear the Drupal cache with Drush
• Use Drush to execute Cron tasks for a Drupal site
• Learn how to use Drush to login to a site as any user, and manage existing users

By the end of this tutorial you'll be able to perform many common Drupal environment and administration tasks from the command line with Drush. We're not going to cover all of the environment management commands in this tutorial, just some of the more popular ones. We encourage you to explore further on your own.