Google seems to have either rolled a new mobile SERP design. I believe that it’s a rollout because I was not been able to get the old interface in different browsers on several different phones. There is still a possibility that it’s a large scale UI test.
The new interface has many differences when compared to the old UI: fonts; font colors; rounded corners; new app installation CTAs, review star colors, and more.
Google was testing various rounded corner interfaces throughout the summer, and it looks like the new interface is finally being pushed to live.
The Desktop UI has not been updated. But knowing that Google likes to provide users with a consistent experience across different devices we can expect the changes there as well.