Direction variants

While a transition runs, the stage carries the class slidev-nav-go-forward or slidev-nav-go-backward. slide.ng adds two UnoCSS variants that use it:

<div class="forward:text-red backward:text-blue">
  Red while a forward transition runs, blue while a backward one runs.
</div>

This works together with a transition on the slide. Without a transition there is no direction to style.