A WordPress child theme is a sub-theme that inherits all the functionality, features, and style of its parent theme. 

A child theme has 3 basic components:

1. style.css file – for your CSS customizations
2. functions.php file – where you can add your custom functions 
3. Screenshot.png – a screenshot of the home page or sometimes, the logo of the theme

When the parent theme gets updated, changes made in the child theme are preserved and applied on the updated version as well, including custom CSS and functions.

In case you are planning to do a lot of customizations, you can download a premade child theme for Botiga by following this link.