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. And then attach that library to a page, or specific element, so that it gets loaded when needed.

In this tutorial we’ll:

• Define what an asset library is.
• Explain why asset libraries are used to include JavaScript and CSS files.
• Look at some example asset library definitions.

By the end of this tutorial you should be able to define what asset libraries are, and when you'll need to create one.

Preprocess functions allow Drupal themes to manipulate the variables that are used in Twig template files by using PHP functions to preprocess data before it is exposed to each template. All of the dynamic content available to theme developers within a Twig template file is exposed through a preprocess function. Understanding how preprocess functions work, and the role they play, is important for both module developers and theme developers.

In this tutorial we'll learn:

• What preprocess functions are and how they work
• The use case for preprocess functions
• The order of execution for preprocess functions

By the end of this tutorial you should be able to explain what preprocess functions are and the role they play in a Drupal theme.

Template files are responsible for the HTML markup of every page generated by Drupal. Any file ending with the .html.twig extension is a template file. These files are composed of standard HTML markup as well as tokens used by the Twig template engine to represent dynamic content that will be substituted into the HTML markup when the template is used. As a theme developer, you'll work with this a lot.

In this tutorial we’re going to learn about:

• What template files are, and how they fit into the big picture of creating a theme
• How template files are used in order to allow theme developers to modify the HTML markup output by Drupal
• Naming conventions for, and specificity of, template files

Themes are the part of Drupal that you, and anyone else visiting your Drupal powered application, see when they view any page in their browser. You can think of a theme as a layer, kind of like a screen, that exists between your Drupal content and the users of your site. Whenever a page is requested Drupal does the work of assembling the content to display into structured data which is then handed off to the presentation layer to determine how to visually represent the data provided.

Drupal themes are created by front-end developer. Frequently referred to as themers, or theme developers. Themes consist of standard web assets like CSS, JavaScript, and images, combined with Drupal-specific templates for generating HTML markup, and YAML files for telling Drupal about the file and features that make up each individual theme.

In this tutorial we'll:

• Explain what a Drupal theme is.
• Explain the role of a Drupal themer in the process of building a Drupal site.
• Get a high level overview of the types of files/code that themes are made of.

By the end of this tutorial you should be able to explain what a Drupal theme is, and the kind of work a Drupal theme developer will be expected to do.

Maybe you've heard of anonymous closures but you're not quite sure how they apply in Drupal, or why using them is considered a best-practice. Anonymous closures allow you to avoid accidentally clashing with anything in the global scope, as well as to alias the jQuery object to the more commonly used $. This is necessary because Drupal runs jQuery in no-conflict mode. This tutorial will look at the syntax used for placing your custom JavaScript code inside an anonymous closure, and why it's a good idea to do so.

In this tutorial we'll:

• Explain what a closure is (briefly), and what immediately invoked function expressions are
• Show how typically Drupal JavaScript gets wrapped in a closure
• Provide a copy/paste example you can use in your own code

By the end of this tutorial you should be able to explain what an anonymous closure is, and how to use one in your custom JavaScript for Drupal.

Like most output in Drupal, Views relies on Twig templates for a significant amount of its rendering. In this tutorial we'll identify where you can find the default Views templates within your file system, what the common templates are for, and how to name your templates so that they are applied to specific views.

By the end of this tutorial, you should be able to:

• Identify where to find default views templates
• Understand which templates apply to what part of a view
• Get a sense of the template suggestions and how to use them to limit where your custom templates are applied
• Identify a view's machine name
• Identify a display's machine name
• Identify a field's machine name

Now that we understand what templates are and how we can use them, let's override some templates! In this tutorial we'll copy the views wrapper template to our theme and override it so that we can customize the markup for the Baseball Players view. Then we'll modify the template so that our view's pager appears both above and below our table of players.

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.

Twig is the theme template engine in Drupal as of version 8. Like any code, there are guidelines and standards that dictate both the style and the structure of the code. In this tutorial we will explain how to adhere to the Drupal code standards while implementing Twig templating.

By the end of this tutorial you will be able to adhere to Drupal's coding standards when writing Twig, and know where to find more information about the guidelines when necessary.

Converting an exisiting theme to Omega takes time and some planning, but Omega gives us plenty of options of moving things around the page all without touching a piece of code. When working with a grid layout we use Omega to set all of our content to span the proper columns all while moving our content from zone to zone so it is placed properly on the page. We will cover:

• Moving content from zone to zone
• Choosing proper zone column widths
• Splitting column amounts to create right and left columns

Once all of this is complete we are just a few steps away from getting into some CSS and really making our theme come together as an Omega sub-theme.

Additional notes:
If you want to touch code, you can edit the .info file as such (for the first part, moving branding zone):

settings[alpha_region_branding_zone] = 'header'
...
settings[alpha_region_branding_weight] = '3'
...
settings[alpha_region_header_first_weight] = '1'
...
settings[alpha_region_header_second_weight] = '2'

Responsive design is more than a just a buzzword these days but a standard practice of good web shops when building out a site. Omega provides a responsive design out of the box and gives lots of options to layout your content in the proper places and the ability to work with the break-points all with a User Interface. In this lesson we will cover:

• Omega responsive options
• Column settings for your grid layout
• Omega responsive layout settings
• Device viewports and media queries

We end the lesson getting our new sub-theme ready to handle our 960 robots theme and the 16 column setup we designed it with.

If you prefer working with code, instead of the web UI, you may configure your theme as follows to change your column settings from 12 grid columns to 16 in your theme's .info file:

Find and replace all the instances of:
_columns] = '12'
with:
_columns] = '16'

There may still be additional regions that also need to be set which weren't the full width. You can edit other regions as needed, such as:
_region_user_first_columns] = '8'
change to:
_region_user_first_columns] = '12'

Walks through the process of first adding the search block to the node template file, and then explains some of the best practices for incorporating JavaScript scripts within your theme. Walks through how to protect the dollar-sign variable, and how to use the Drupal behaviors instead of the document ready so that your JavaScript will fire not only on page loads, but also if there is any dynamic material being loaded on the page through asynchronous page loads. We'll show you how to select the jQuery selector to target the desired element, and how to conform to Drupal's best-practice coding standards when it comes to integrating JavaScript and jQuery into your theme. You can learn more about jQuery itself with the Introduction to jQuery Series.

To use Query in no conflict mode, because was not defined.
Add this line on the top: jQuery.noConflict(); more info here: http://api.jquery.com/jQuery.noConflict/

To improve how the search box looks, you need to modify the following:
currently : search-theme-form
modify to: search-block-form
and then in the property in line 321 to look like this:

/* Header quick search */
#header form#search-block-form {
    top: -165px;

Additional resources

Introduction to jQuery Series

Shows how you can use the ajax framework in Drupal 7 to load additional content onto the page dynamically after clicking on a 'read more' link.

The sample code for this series is in the Downloads tab for the first video in this series: http://drupalize.me/videos/introduction-jquery-and-javascript-drupal#do…. If you're skipping around, and things aren't working, you may benefit from going back to the beginning and completing each of the videos in order.

Emma Jane Westby introduces the series. In this series, you'll learn how to transform a static design file into a whole Drupal theme. We'll work through three major steps.

1. Develop a style guide based on the design patterns we see in our design files.
2. Build out Drupal so that it has all of the elements we need in place.
3. Work with theming files to decorate Drupal.

Additional Resources

In addition to the lessons in this series, Emma has assembled an extensive FAQ on Drupal theming.

In this lesson we'll take a tour of the theme you'll be building. The design we'll be working with was created by Betty Bisenthal. It's a fairly simple design with three columns and a banner image. It has been used as a starting point for several years by many people who are learning to theme. In this lesson we'll take a look at:

• the design we'll be working with
• variations of this design created by other students
• how Drupal was customized to accommodate our design
• the Sass used to create the layout for the site

By the end of this lesson you'll be able to describe the shape of the design used throughout this series, and identify variants of the design.

Additional resources

Domicile theme

Nine Sixty base theme

KidActive site

Digitise the Dawn

In this lesson we're going to learn about the front end development strategy of theming by components. This strategy relies on being able to break a design into individual components. Elsewhere on the Web this technique has been described as “atomic design” or “interface pattern pairing”. No matter what you call it, developing a pattern library of components is going to make it a lot easier to convert your design to a theme. This is an overview lesson that explains the strategy we'll be using in future lessons. More specifically, we'll look at:

• two popular pattern libraries
• an overview of how pages are built by Drupal so they can be rendered in a browser

By the end of this lesson you'll be able to identify components from a static design file by referencing a pattern library.

Additional resources

Atomic Design

SMACSS (Scalable and Modular Architecture for CSS)

Balsamiq Mockups

Over the last couple of years we've seen the rise of object oriented CSS. There's been a lot of work done by smart folks to categorize different types of rules that we use to style our sites. We're going to take advantage of this work and use it to create a style guide. This foundation piece will help us to map the elements in our static design to the elements that we will build, and theme, in Drupal.In this lesson we'll create a style guide from our design with:

• Base rules
• Layout rules
• Component rules

By the end of this lesson you will be able to create a text-based style guide of your design which accurately describes your site according to base rules, layout rules, and component rules. You will be able to further supplement this style guide by adding relevant images which reference the exact component the style guide is describing.

In the previous lesson you created a text-based style guide. It's now time to extract the necessary assets from our static design for use in our theme. To complete this lesson you will need a design application capable of opening a .psd file. The video demonstrates Photoshop, but I typically use Gimp. Either is fine. And if you don't have a graphics program, you can watch the video, but simply download the assets which were extracted during the lesson. By the end of this lesson you will be able to identify page-level design assets which need to be extracted from a design file for your Drupal theme.

Additional resources

Gimp

Photoshop

Pixelmator