re-transition-css>` object. In the above example, `<my-css-transition>` implements both
sliding the node from the top of the viewport and from the bottom of the viewport.

Available transitions
---------------------

`<core-transition-css>` includes several commonly used transitions.

`core-transition-fade`: Animates from `opacity: 0` to `opacity: 1` when it opens.

`core-transition-center`: Zooms the node into the final size.

`core-transition-top`: Slides the node into the final position from the top.

`c