To get started with these new ad shapes, visit the 'AdSense Setup' tab in your account. As with all format options like sizes and colors, different corner styles will perform better for different publishers. We recommend that you choose the corner style that best matches the look and feel of your sites. Please keep in mind that if your page background color, ad background color, and ad border color are all the same, these new corners won't be visible.
This new option is part of our ongoing effort to improve the look and feel of our ads. We're also working to give you even more choices to customize your ad formats while maximizing revenue and user satisfaction. We hope you enjoy the new corner options, whether you choose to go edgy or bubbly.
-searchspiderz