This change removes the erroneous `border-color: gray` CSS rule from the UA stylesheet for the `<table>` element. The spec does not contain this rule: https://html.spec.whatwg.org/multipage/rendering.html#tables-2 and it causes the borders to incorrectly not default to currentColor. Neither Firefox nor Webkit have this `gray` border color rule in their UA stylesheet, leading to interop problems.
The current hard-coded gray color is not interoperable, and does not match the spec.