I'm no expert but I think the correct CSS is
page-break-after: avoid over the heading title.
I mean if you have:
Code:
<h2 class="title">My heading</h2>
<p>The paragraph I want to keep in the same page than "My title".</p>
You have to put something like:
Code:
.title {
... ;
... whatever other settings it already has... ;
... ;
page-break-after: avoid;
}
(Although take in mind that this setting does not always work. As a really frustrating evidence, Kobo ACCESS renderer completely ignores it, so there's no way to keep the titles and their following paragraph in Kobo kepubs).
And take in mind that .
block_ doesn't match ANYTHING. You must type it complete (
.block_17 or whatever)