Try creating a CSS style rule something like:
Code:
.negative {background-color: #000; color:#fff}
Then wrap the text sections you want to be white-on-black with a <div class="negative">. Like this:
Code:
<div class="negative">
<p>Paragraph 1 in reverse</p>
<p>Paragraph 2 in reverse</p>
... etc ...
</div>
If you want the whole of a "chapter" to be white-on-black then try adding the negative class to the <body> tag instead, i.e. <body class="negative">
Caveat: If you intend to read on a device which has a "Night Mode" you might need to test the results in advance.