The way I do it works perfectly well in ePub and KF8/KFX.
HTML
Code:
<p>Some line.</p>
<hr/>
<p class="noindent">Some other paragraph.</p>
CSS
Code:
body {
widows: 1;
orphans: 1;
margin-top: 0;
margin-right: 0;
margin-bottom: 0;
margin-left: 0;
text-align: justify;
}
hr {
margin-top: 0.9em;
margin-right: 40%;
margin-bottom: 0.9em;
margin-left: 40%;
border-top: 2px solid;
}
p {
margin-top: 0;
margin-bottom: 0;
widows: 1;
orphans: 1;
text-indent: 1.2em;
}