Ports the same approach from https://github.com/twbs/bootstrap/commit/1f153b640de55a4fff1aca3cf7331e9b7e3a408f#diff-edb9cd89b66120ef946a81de31f6bb06 (originally https://github.com/twbs/bootstrap/pull/16154 in v3) to outline buttons as well
Ports the same approach from https://github.com/twbs/bootstrap/commit/1f153b640de55a4fff1aca3cf7331e9b7e3a408f#diff-edb9cd89b66120ef946a81de31f6bb06 (originally https://github.com/twbs/bootstrap/pull/16154 in v3) to outline buttons as well