Add hooks for styling lists of divs.

This is so we can do styling like:

```css
.wafer.list div:nth-child(2n) {
  background: rgba(0, 0, 0, 0.1);
  padding: 10px;
}

.wafer.list div:nth-child(2n + 1) {
  background: rgba(255, 255, 255, 0.1);
  padding: 10px;
}
```