After maintaining a sensible, orderly division of the various elements on the page, we move on to the styling stage - and here too we want to keep to the required minimum, with clean and simple code.
The basic styling options for our element tags are:
1. INLINE style definitions - where the style definitions are written in the style attribute of the tag itself.
2. CSS definitions in classes - where the style definitions are written in an external CSS file and linked via the tag's class attribute.
Usually we will choose the second option, in order to keep identical styling for identical paragraphs and text.
In a regular text-based book, most of the text segments will be styled identically, and so with a small number of classes we can style most of the book. This is a technique that produces clean, simple code. One class for the heading, one class for the chapter's main text, and perhaps a few more if there are indents, quotations, or special styles that require it.
Of course we will not use the first option to style the entire book - that would lead to duplicating the styling code for each paragraph separately, would burden the app, and would even make future fixes or upgrades harder.
But there is one special tag that you should pay particular attention to. The body tag.
This tag wraps the entire text of the chapter, all the other visual tags in the chapter, and hence its importance.
Because this tag is the root of all the other tags, most reading apps make deliberate use of it to change the style settings for the chapter and the whole book - according to the reader's own choices. And this is where a problem can arise...
Because the reading app directly affects the root tag, the body tag, in order to apply the user's style settings - here, in this tag specifically, it is recommended not to use the class method and in fact to avoid any styling element that could conflict with the user's and the app's settings.
If there is a particular style you do want to apply to the whole page, on the main body tag, it is better to do so with an INLINE style definition, to ensure the style is kept at high priority and also so as not to interfere with the app's style settings, which are applied via predefined CSS classes.