Follow bellow steps
step : 1 (theme.xml)
<theme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/theme.xsd">
<title>Magento Apple</title>
<parent>Magento/luma</parent>
<media>
<preview_image>media/preview.jpg</preview_image>
</media>
</theme>
Step : 2 (registration.php)
<?php
/**
* Copyright © 2015 Magento. All rights reserved.
* See COPYING.txt for license details.
*/
\Magento\Framework\Component\ComponentRegistrar::register(
\Magento\Framework\Component\ComponentRegistrar::THEME,
'frontend/Magento/Apple',
__DIR__
);
Step : 3 composer.json
{
"name": "magento/theme-frontend-apple",
"description": "N/A",
"require": {
"php": "~5.5.0|~5.6.0|~7.0.0",
"magento/theme-frontend-luma": "100.0.*",
"magento/framework": "100.0.*"
},
"type": "magento2-theme",
"version": "100.0.2",
"license": [
"OSL-3.0",
"AFL-3.0"
],
"autoload": {
"files": [
"registration.php"
]
}
}