Why not write simply this :
Code:
<h2>Chapter 1<br/><span class="small">Title of C1</small></h2>
...
<h2>Chapter 2<br/><span class="small">Title of C2</small></h2>
...
with in styles.css :
Code:
span.small{
font-size: 90%;
/* or the whole character format you want to give to h3 */
}