- `align-items`: `normal` is the initial value in the CSS-ALIGN spec,
but `stretch` is in CSS-FLEXBOX. The FLEXBOX spec is the one we've
actually implemented elsewhere, and ALIGN adds new values with special
syntax, so it's not trivial to add it here.
- `border-spacing`: `0` is equivalent to `0px 0px` and we don't yet
parse the double-value syntax.
- `text-decoration-thickness`: Had the wrong value.