Lets us create a child theme so our all custom themes in Magento 2 goes here:
app/design/frontend/company_name/theme_name
Let us assume, our company name is mycompany and our theme name is basic. We need to create following directory structure for our theme:
app
└────design
└──────frontend
└──mycompany
└───basic
└──etc
└──Magento_Theme
│ └─layout
│ default.xml
└──media
│ preview.png
└──web
│ └─css
│ └─fonts
│ └─images
│ └─js
│ theme.xml
│ registration.php
mycompany :-
The name of the theme package
basic :-
The name of the theme. We can have multiple named themes inside the mycompany folder.
etc/view.xml :-
This file is used to specify product image dimensions, thumbnails etc.
Magento_Theme :-
This directory is used to override existing Magento’s theme files.
Magento_Theme/layout/default.xml :-
By default Magento2 assumes that your theme’s logo file should be: /web/media/logo.svg
If you want some other file for logo, then you must declare it in default.xml
file.
This file is also used to override default theme’s settings.
media/preview.png :-
The preview of current theme.
web :-
This directory contains all the theme’s static data like images, styles, javascript, fonts etc.
registration.php :-
This file is required to register our theme to Magento2 system.
theme.xml :-
This is a compulsory file that defines our theme name, its parent and optionally theme’s preview image.
Creating theme files
Let us now create our files one by one.
theme.xml ( app/design/frontend/mycompany/basic/theme.xml )
<theme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/theme.xsd">
<title>Basic</title> <!-- your theme's name -->
<parent>Magento/blank</parent> <!-- the parent theme -->
<media>
<preview_image>media/preview.jpg</preview_image> <!-- theme's preview image -->
</media>
</theme>
registration.php ( app/design/frontend/mycompany/basic/registration.php )
<?php
\Magento\Framework\Component\ComponentRegistrar::register(
\Magento\Framework\Component\ComponentRegistrar::THEME,
'frontend/mycompany/basic',
__DIR__
);
default.xml ( app/design/frontend/mycompany/basic/Magento_Theme/layout/default.xml )
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
<body>
<referenceBlock name="logo">
<arguments>
<argument name="logo_file" xsi:type="string">images/my_logo.png</argument>
<argument name="logo_img_width" xsi:type="number">200</argument>
<argument name="logo_img_height" xsi:type="number">200</argument>
</arguments>
</referenceBlock>
</body>
</page>
At this point, our theme is ready. Clear your cache and we will now select our new theme from admin.
Now, login to admin and move to following path:
Content -> Design -> Themes
You should see your theme listed.
Now go to:
Stores -> Configuration -> Design
Choose Main Website in front of Store View at top left. Now click
Desgin -> Design Theme
Uncheck Use Default checkbox and pick your theme. Click Save Config, clear your cache and your new theme is ready. Check your home page.
For more detail see here.