Fix some ObjectItemList issues

Summary:
Safari has a weird bug with `border-radius` plus border color:

{F35865}

Move the uncolored borders to an internal div to fix this. Also tweak some positioning on icons for cards, and add a "magenta" color.

Test Plan: {F35866}

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D5338