Fix inline highlight behaviors for Pholio

Summary:
Some recent CSS change tweaked these out a bit. They were also sort of weird looking after fixing the double-draw thing:

  - Make them work properly;
  - make the implementation a bit simpler;
  - make them clearer visually.

Also fix a bug where "border" and "fill" were accidentally reversed.

Test Plan:
{F34625}

(The highlight on the reticle is a little hard to pick out in the screenshot, but very obvious in practice.)

Reviewers: chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D5228