Delta child theme: install and use it in WordPress

A child theme is a small theme that runs on top of Delta. It holds files that belong to one site, and a Delta update never overwrites them.

Most Delta sites don’t need one. Pages, templates, design tokens and site CSS are stored in the database and uploads, and an update leaves them alone. Use a child theme when something has to be a file: a PHP hook, a stylesheet you keep in version control, or an override of one of Delta’s PHP templates.

What you need

Delta installed and its license active. See Install and activate.
Delta in a folder named delta, which is what the release ZIP creates.

Install it

Download delta-child.zip. Use this file, not GitHub’s “Source code” archive, because that folder name carries the version number.
In wp-admin, go to Appearance → Themes → Add New Theme → Upload Theme, and upload the file.
Activate Delta Child.

Delta opens Delta → Connect after activation. Appearance → Themes now shows Active: Delta Child, and you don’t enter the license again.

To install with WP-CLI instead:

wp theme install https://github.com/21press/delta-child/releases/latest/download/delta-child.zip --activate

What stays the same

The child theme uses all of Delta’s code, so Delta’s menu, the Front panel and your agent connection keep working. Your pages, templates and design system stay as they were. The site logo, menu locations and Additional CSS carry over.

Where each change goes

Change	Where
Pages, templates, tokens, site CSS	Through the agent, as before
PHP hooks and filters	`functions.php` in the child theme
CSS you want to keep in a file	`style.css` in the child theme
A replacement for one of Delta’s PHP templates	A file with the same name in the child theme, such as `404.php`

How the CSS loads

The child style.css loads after site.css and the header and footer CSS, and before the CSS of the current page or template. When a child rule and a page rule have the same specificity, the page rule wins. Design tokens work in the child stylesheet as var(--name).

Tell the agent about it

Delta’s abilities read and write pages, templates and the design system. They don’t read theme files, so the agent doesn’t see your child theme. Record what it does in the design notes, so the next session knows:

“Add to the design notes: the child theme’s style.css holds {what it holds}.”

Updates

Delta keeps updating through its license. The child theme doesn’t update itself, because it holds your own code. To take something from a later version of the starter, read the changelog and copy the change by hand.

If something goes wrong

The upload shows The parent theme could not be found. and no Activate link: WordPress can’t find Delta in a folder named delta. Install Delta, then activate Delta Child under Appearance → Themes. If Delta’s folder has another name, change Template: delta in the child style.css to that name.
A CSS rule has no effect: page or template CSS is overriding it. Raise the rule’s specificity, or change the page’s CSS through the agent.
The site breaks after a PHP change: switch back to Delta under Appearance → Themes. Your pages, templates and design system stay in place, and the child theme’s code stops running.

For developers

WordPress loads the child functions.php before Delta’s, so Delta’s constants and classes don’t exist at the top of the file. Put code that needs them inside a hook such as after_setup_theme or init.

To add a script:

add_action( 'wp_enqueue_scripts', function () {
	wp_enqueue_script( 'delta-child', get_stylesheet_directory_uri() . '/script.js', array(), '1.0.0', array( 'in_footer' => true ) );
}, 20 );

The source is at 21press/delta-child, under GPLv2 or later.

Child theme