2.1.2 Create a Complicated Child Theme

/*
Theme Name: Twenty Sixteen – Child
Theme URI:
Description:
Author:
Author URI:
Template: twentysixteen
Version:
License:
License URI:
Tags:
Text Domain:
*/

Enqueue the parent and child theme stylesheets because using @import increases the amount of time it takes style sheets to load.

add a wp_enqueue_scripts action in a function.php file

functions.php

 

Setting ‘parent-style’ as a dependency will ensure that the child theme stylesheet loads after it.

Including the child theme version number ensures that you can bust cache also for the child theme. See a more detailed discussion on Stack Exchange:

versioning-import-of-parent-themes-style-css

The complete (recommended) example becomes:

where |parent-style| is the same |$handle| used in the parent theme when it registers its stylesheet.

For example, if the parent theme is twentyfifteen, by looking in its functions.php
for its |wp_enqueue_style()| call, you can see the tag it uses there is |’twentyfifteen-style’|. In your child code, replace the instance of |’parent-style’| with |’twentyfifteen-style’|, like so:

$parent_style = ‘twentyfifteen-style’;

Failure to use the proper tag will result in a CSS file needlessly being
loaded twice. This will usually not affect the site appearance, but it’s
inefficient and extends your page’s loading time.

*Note:* You may need to re-save your menu (Appearance > Menus, or
Appearance > Customize > Menus) and theme options (including background
and header images) after activating the child theme.

codex.wordpress.org/Child_Themes