Child Themes

Hi, All:

So, I have been hired to make some changes to an existing site built by someone else about 5 years ago. They are happy with most aspects of the site’s appearance, but want me to tweak a few things here and there.

Well, the person who created it did not make a child theme and the theme is about 10 updates behind.

Not knowing what changes were made to the css and various php files of the theme back when the site was built, I am not sure how to create a child theme. Could I copy all current php and css douments into a child theme folder? I know that is not a best practice, but I am unsure how to proceed.

Of course, I could just leave it as is and not update the theme. I am thinking it will eventually stop working with updated WP.

Advice is appreciated.