If you are using a WordPress.org theme that doesn’t come with the option of a child theme, or an editable separate style sheet, then it is recommend to use a child theme.
Why? Well if you intend to edit the style sheet, when you update your theme it is likely those edits will be written over.
A child theme sits in your theme folder, and it lets you just add the code for the bits your want to change on your site. Instead of wading through the whole style sheet looking for a colour code. This is especially handy as you can easily see what changes you have made instead of editing and then not being able to find it.
Here are the steps I used to set up a child theme using the Divi theme from Elegant Themes themes.
I added the theme to WordPress via the WordPress dashboard as usual, then via ftp I added a new folder in the themes directory ‘DiviChildF’ So click into your WordPress folder in your directory then,
I copied the style.css file from the Divi theme folder to the DiviChild.
I edited the contents of the style.css file in the child folder to be just the below in red.
I simply keep the code in red saved on my computer and copy and paste it into a text file and save it every time I set up a new site using Divi
Theme Name: Divi Child Theme
Theme URI: http://www.elegantthemes.com/gallery/divi/
Description: Divi Child Theme
Author: Elegant Themes
Author URI: http://www.elegantthemes.com
/* =Theme customization starts here
Now log into your WordPress dashboard and under Appearance – themes you will see your child theme.
Then if you want to change any of the site style simply go to Appearance – Editor and add the code under the info already there. And you will see that it changes on your site.
The child theme takes all the other theme code / documentation / files from the parent theme, so you need to update the parent.