It would be easy enough to hide this button by default and just `return` here.

```js
if (!this._isSupportedAction(newAction)) {
  this._button.removeAttribute('action');
  return;
}
```

Then is the CSS we can just have a rule like:

```css
#action-button[action] {
  display: block;
}
```

So the action button only shows if an action attribute has been set on it. Might even be nicer to set all the attribute state a little higher up in the same place, on `<section>` or `<header>`.