Create a CSS file name style.css file on Qoxag-child\style.css folder and write your own CSS customization.

Some Charectaristics of the style.css file 

The file is included by default
The file is the last file to be loaded in your site.

What is a Child Theme?

As indicated in the overview, a child theme inherits the look and feel of the parent theme and all of its functions, but can be used to make modifications to any part of the theme. In this way, customizations are kept separate from the parent theme’s files. Using a child theme lets you upgrade the parent theme without affecting the customizations you’ve made to your site.

Child themes:

1. make your modifications portable and replicable;
2.keep customization separate from parent theme functions;
3.allow parent themes to be updated without destroying your modifications;
4. allow you to take advantage of the effort and testing put into parent theme;
5.save on development time since you are not recreating the wheel; and
6.are a great way to start learning about theme development.