A child theme allows you to change small aspects of your site’s appearance yet still preserve your theme’s look and functionality. To understand how child themes work it is first important to understand the relationship between parent and child themes.
A parent theme is a complete theme which includes all of the required WordPress template files and assets for the theme to work. All themes – excluding child themes – are considered parent themes.
As indicated in the overview, a child theme inherits the look and feel of the parent theme and all of its functions, but can be used to make modifications to any part of the theme. In this way, customizations are kept separate from the parent theme’s files. Using a child theme lets you upgrade the parent theme without affecting the customizations you’ve made to your site.
Child themes:
1. make your modifications portable and replicable;
2. keep customization separate from parent theme functions;
3. allow parent themes to be updated without destroying your modifications;
4. allow you to take advantage of the effort and testing put into parent theme;
5. save on development time since you are not recreating the wheel; and
6. are a great way to start learning about theme development.
- Create a child theme folder
First, create a new folder in your themes directory, located at wp-content/themes.
The directory needs a name. It’s best practice to give a child theme the same name as the parent, but with -child appended to the end. For example, if you were making a child theme of twentyfifteen, then the directory would be named twentyfifteen-child.
- Create a stylesheet: style.css
Next, you’ll need to create a stylesheet file named style.css, which will contain all of the CSS rules and declarations that control the look of your theme. Your stylesheet must contain the below required header comment at the very top of the file. This tells WordPress basic info about the theme, including the fact that it is a child theme with a particular parent.
/*
Theme Name: Twenty Fifteen Child
Theme URI: http://example.com/twenty-fifteen-child/
Description: Twenty Fifteen Child Theme
Author: John Doe
Author URI: http://example.com
Template: twentyfifteen
Version: 1.0.0
License: GNU General Public License v2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html
Tags: light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
Text Domain: twentyfifteenchild
*/
The following information is required:
Theme Name – needs to be unique to your theme
Template – the name of the parent theme directory. The parent theme in our example is the Twenty Fifteen theme, so the Template will be twentyfifteen. You may be working with a different theme, so adjust accordingly.
Add remaining information as applicable. The only required child theme file is style.css, but functions.php is necessary to enqueue styles correctly (below).
- Enqueue stylesheet
The final step is to enqueue the parent and child theme stylesheets, if needed.
The ideal way of enqueuing stylesheets is for the parent theme to load both (parent’s and child’s), but not all themes do this. Therefore, you need to examine the code of the parent theme to see what it does and to get the handle name that the parent theme uses. The handle is the first parameter of wp_enqueue_style().
There are a few things to keep in mind:
1. the child theme is loaded before the parent theme.
2. everything is hooked to an action with a priority (default is 10) but the ones 3. with the same priority run in the order they were loaded.
4. for each handle, only the first call to wp_enqueue_style() is relevant (others ignored).
5. the dependency parameter of wp_enqueue_style() affects the order of loading.
6. without a version number, site visitors will get whatever their browser has cached, instead of the new version.
7. using a function to get the theme’s version will return the active theme’s version (child if there is a child).
8. the functions named get_stylesheet* look for a child theme first and then the parent.
The recommended way of enqueuing the stylesheets is to add a wp_enqueue_scripts action and use wp_enqueue_style() in your child theme’s functions.php. If you do not have one, create a functions.php in your child theme’s directory. The first line of your child theme’s functions.php will be an opening PHP tag (<?php), after which you can write the PHP code according to what your parent theme does.
If the parent theme loads both stylesheets, the child theme does not need to do anything.
If the parent theme loads its style using a function starting with get_template, such as get_template_directory() and get_template_directory_uri(), the child theme needs to load just the child styles, using the parent’s handle in the dependency parameter.
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles' );
function my_theme_enqueue_styles() {
wp_enqueue_style( 'child-style', get_stylesheet_uri(),
array( 'parenthandle' ),
wp_get_theme()->get('Version') // this only works if you have Version in the style header
);
}
If the parent theme loads its style using a function starting with get_stylesheet, such as get_stylesheet_directory() and get_stylesheet_directory_uri(), the child theme needs to load both parent and child stylesheets. Be sure to use the same handle name as the parent does for the parent styles.
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles' );
function my_theme_enqueue_styles() {
$parenthandle = 'parent-style'; // This is 'twentyfifteen-style' for the Twenty Fifteen theme.
$theme = wp_get_theme();
wp_enqueue_style( $parenthandle, get_template_directory_uri() . '/style.css',
array(), // if the parent theme code has a dependency, copy it to here
$theme->parent()->get('Version')
);
wp_enqueue_style( 'child-style', get_stylesheet_uri(),
array( $parenthandle ),
$theme->get('Version') // this only works if you have Version in the style header
);
}
- Install child theme
Install the child theme as you install any other theme. You can copy the folder to the site using FTP, or create a zip file of the child theme folder, choosing the option to maintain folder structure, and click on Appearance > Themes > Add New to upload the zip file.
- Activate child theme
Your child theme is now ready for activation. Log in to your site’s Administration Screen, and go to Administration Screen > Appearance > Themes. You should see your child theme listed and ready for activation. (If your WordPress installation is multi-site enabled, then you may need to switch to your network Administration Screen to enable the theme (within the Network Admin Themes Screen tab). You can then switch back to your site-specific WordPress Administration Screen to activate your child theme.)
Other than the functions.php file (as noted above), any file you add to your child theme will overwrite the same file in the parent theme.
In most cases, it’s best to create a copy of the template files you want to change from the parent theme, then make your modifications to the copied files, leaving the parent files unchanged. For example, if you wanted to change the code of the parent theme’s header.php file, you would copy the file to your child theme folder and customize it there.
You can also include files in the child theme that are not included in the parent theme. For instance, you might want to create a more specific template than is found in your parent theme, such as a template for a specific page or category archive (e.g. page-3.php would load for a Page with the ID of 3).
See the Template Hierarchy page for more information about how WordPress determines which template to use.
Unlike style.css, the functions.php of a child theme does not override its counterpart from the parent. Instead, it is loaded in addition to the parent’s functions.php. (Specifically, it is loaded right before the parent’s file.)
In that way, the functions.php of a child theme provides a smart, trouble-free method of modifying the functionality of a parent theme. Say that you want to add a PHP function to your theme. The fastest way would be to open its functions.php file and put the function there. But that’s not smart: The next time your theme is updated, your function will disappear. But there is an alternative way which is the smart way: you can create a child theme, add a functions.php file in it, and add your function to that file. The function will do the exact same job from there too, with the advantage that it will not be affected by future updates of the parent theme. Do not copy the full content of functions.php of the parent theme into functions.php in the child theme.
The structure of functions.php is simple: An opening PHP tag at the top, and below it, your bits of PHP. In it you can put as many or as few functions as you wish. The example below shows an elementary functions.php file that does one simple thing: Adds a favicon link to the head element of HTML pages.
<?php // Opening PHP tag - nothing should be before this, not even whitespace
// Custom Function to Include
function my_favicon_link() {
echo <link rel="shortcut icon" type="image/x-icon" href="/favicon.ico" />' . "\n";
}
add_action( 'wp_head', 'my_favicon_link' );