At present the information in the Codex is too scattered, too disorganized, and incomplete. In short, NEI (Not Enough Information). To sum up; about as clear as Ukraine mud.
The Codex needs reorganizing, clairification, and expansion.
For style sheets and templates I suggest the following sections.
Creating a Style Sheet
...Creating a Child Style Sheet
Modifying a Style Sheet, parent or child
Creating a Template
Adding a template
Modifying a template.
Important: Put all relevant information on the same page. Everything a person needs to know when creating or modifying a Style Sheet. Everything a person needs to know when creating, adding, or modifying a template.
Keep in mind that not everybody knows what you know.
Also that not everybody has your amazing memory. (Add a form that let's people save what they just read, so it can serve as a reminder)