Copy of luma theme

The following steps describe how to create New Magento 2 theme from the existing Magento Luma theme and its implementation.

Create a new Vendor folder inside app/design/frontend/NewVendorName (ex: DCKAP). The folder will be like this – app/design/frontend/DCKAP.
Create theme folder inside your Vendor folder app/design/frontend/DCKAP/theme-new
Next, navigate to vendor\magento\theme-frontend-luma
Copy entire folder and files inside “theme-frontend-luma” into your theme folder (i.e.) app/design/frontend/DCKAP/theme-new/
Edit app/design/frontend/DCKAP/theme-new/registration.php file and change as following ‘frontend/Magento/luma’ to ‘frontend/DCKAP/new’.
Next Edit app/design/frontend/DCKAP/theme-new/theme.xml file and change the title as per your identification.
Once done save and close the file.

<theme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/theme.xsd">

<title>Dckap New</title>

<parent>Magento/blank</parent>

<media>

<preview_image>media/preview.jpg</preview_image>

</media>

</theme>

Finally, clear var/cache and var/page_cache before logging into Magento 2 Admin.
Navigate to Stores->Configuration->Design->Design Theme.
Select your newly created theme “Dckap New”. Save the configuration.

Refresh the frontend and you will be able to view your design from newly allocated theme.

To make sure please view ‘Page Source’ which will display the CSS and js URL path as per your registration.php configuration file.

Source: http://www.dckap.com/blog/creating-magento-2-theme/

How to Create a Magento 2 Theme?