Give a fragment link an up-transition attribute to animate between
the old and new fragment.
<main>
<h1>The first story</h1>
<a href="story2.html" up-transition="move-left" up-follow>
Show next story
</a>
</main>
<main>
<h1>The second story</h1>
<a href="story1.html" up-transition="move-right" up-follow>
Show previous story
</a>
</main>