A child theme consists of at least one directory (the child theme directory) and two files (style.css and functions.php), which you will need to create:
- The child theme directory
If your child theme shows error: “The parent theme is missing. Please install your parent theme”. There are three things to check:
1 – Is your parent theme complete and what is the exact spelling of the parent theme’s name in its style.css. Uppercase and lowercase are important.
2 – Is the child theme directory named parentname-child. It should be in the themes directory, not in a subdirectory of the parent theme.
3 – Does the child theme’s style.css have the line Template: parentname in its header. Beware: NOT Template: parentname-child.
More information: https://codex.wordpress.org/Child_Themes