DC's Rebirth initiative has two goals, which at first seem at odds with each other, but seem to be working so far. The first is to shake up the majority of their line, taking their books in new directions that feel fresh. The other is to make it feel more like the pre-New 52 DC Universe by bringing back fan favorite characters, iconic outfits, and popular backstories. I guess there's also a third category that falls in between these two, which is adjusting their books to better match popular adaptations. This falls under that third category.
Vixen has been featured on this site before for her wardrobe changes. You can read about that here. That post will bring you up to the New 52, but shortly after that, Vixen got an animated series on CW Seed (August 2015). So while in the comics she looked like this:
On the show she looked like this:
The series turned out to be fairly popular, to the point that the character made a live action appearance on Arrow, played by her voice actor. Another Vixen, the first Vixen's grandmother, appeared this season on Legends of Tomorrow as a member of the Justice Society. With all that exposure, it makes sense to update her costume again (especially to get rid of that plunging neckline), so in DC Rebirth #1 (May 2016), we got this:
Which was modified a little into this in Justice League of America: Vixen #1 (January 2017):