Make named anchor/placeholder link style reset more specific

Make named anchor/placeholder link style reset more specific

This avoids applying the reset to named anchors/placeholder links (links
without an `href`) that have explicitly been made keyboard-focusable
(using `tabindex`). This is not fool-proof - it's not
easy/straightforward to check for the actual `tabindex` value itself, to
ensure it's positive, not will this apply if a link has been "blessed"
with `tabindex` via JS. However, this should catch most common uses (and
gives a reasonably valid way around the issue for developers who, for
whatever reason, DO want to use links without `href` - as side effect,
it forces best practice of at least ensuring these links can also be
focused with the keyboard)