Google announced that they have launched a new default ad unit style that works better across all devices, mobile to desktop.

The changes include:

A new default color palette of blue and grey, making the ads easier to read for the user
An updated our default font to Roboto, designed for easier readability on mobile devices as well as desktop.
They aligned the text ad font with the web font they use on our Android OS.
Improved the call-to-action button by making the tap target size and position more user-friendly across devices

Here is one sample ad but you can see more over here.

Forum discussion at Google+.