Rendering bugs on docs.rs

The following bugs/screenshots are from:

- https://docs.rs/taffy/0.7.6/taffy/index.html
- Rendered with Blitz commit `0262318f0e51d4c943b39c74c91870e091dbb4f4`

### Task list

- [ ] Navigation icons are misaligned
- [x] Header is layout in garbled
- [x] Sidebar labels are cut off
- [x] Item grid is completely messed up

### Navigation icons are misaligned

This is due to missing vertical-align style (needs to be implemented in Parley)

### Header is layout in garbled

This is due to missing named grid areas

### Sidebar labels are cut off

This is due to the clip being miscalculated when rendering. If I remove the clipping then this renders correctly. May have to do with negative margins and/or borders as this HTML uses both of those features.

### Item grid is completely messed up

Not sure what's going on here. But it is using CSS Grid layout and seems to be mispositioning items completely wrong. Unclear whether this is a placement or sizing bug. Could be related to the Flexbox layout on servo.org being too wide.