IE11 shows Share modal offset to the right instead of centered

[robwhitaker]

This doesn't occur when the flex styles on the modal div are disabled. Somehow, the external flex container affects the div properly when it isn't set to be treated as a flex element. Of course, disabling the flex styles breaks the positioning in every other browser.

[robwhitaker]

This was incorrectly closed by a commit message. @larouxn