Yeah, your post clearly has nothing to do with errant tabs, but I strongly suspect the other issue is related to that. Tabs don’t do anything meaningful in HTML anyway.
All right, so I’ve had a look at the source, and the problem has to do with poor HTML output, basically. Here is what you get when applying a style like this:
<p class="citation"><em><span class="citation">Blah blah...</span></em></p>
So there are two problems with that. One is that the span is entirely unnecessary since all of that formatting can be applied directly to the paragraph. There is hardly ever a need to wrap an entire paragraph in a span like that. The <em> is also unnecessary of course, since the .citation class itself can and does define italics. But these could be brushed aside as redundant styling—where it becomes problematic is when you add CSS like this:
.citation {
margin: 0rem 0rem 0rem 3rem;
text-indent: 0rem;
/* etc. */
}
You may be able to spot the issue, since both the paragraph and the text within the paragraph is classed as .citation, both get a left margin offset of 3rem. One indents the whole paragraph block, the other indents the text within the paragraph block, creating what looks like a first-line indent, even though we have that set to zero.
So one way of solving this is to add the following to the CSS compile format pane:
.citation .citation { margin: 0rem 0rem 0rem 0rem; }
That’s probably the best workaround, because once this bug gets fixed the CSS will end up doing nothing, and you won’t have to go back and change anything. It also allows you to continue using your style the way you want in the editor.
The other workaround would be to make the style paragraph-only, and add the character level formatting you want (text colour, italics, etc.) into the CSS pane yourself. But then these will just look like indented text in the editor.
Debugging Mobi Files...
As for examining Mobi output, I don’t know if there are any editors or even viewers that can examine these files more closely. What is best to do is to go into your general options tab in the compiler, and enable the setting that exports the source files along with the .mobi. That’s exactly what Scrivener hands off to KindleGen, so you can see what’s going on, and you can even make tweaks to the source files, and drop the .opf file into KindlePreviewer to have it assemble a preview for you.
So that’s what I’d suggest doing, so you can see exactly what CSS Scrivener is generating for the .citation class, and examine the DOM and interactions with any other CSS that may be impacting it, using your brower’s page inspection tools.
Kindle Previewer includes KindleGen, and that’s what we’re using to make the conversion.