It makes sense to me the way it works.
It works on a single Element (
http://www.w3.org/TR/1999/REC-html40...t.html#h-3.2.1 )
IMHO 3 sequential headings is odd and an alternate coding might be better.
Code:
<h3 class="chapter">42<br /><span class="chaptitle">The Title</span><br /><span class="chapsubt">subtle title :)</span></h3>
Bold, italic and those kinds of things are Phrase Elements and it is more common to have them applied to multiple elements.
Some day, we may see Sigil get the ability to 'set' (as in attach) a CSS selector interactively to those buttons via a right click with the default being the present SGC way.
scenario:
right-click the [P]: (multi: in the preferred order?) choose a selector (the burden is on the user to pick sensible ones)
ex: firstpara and bolditalic = <p class="firstpara bolditalic">