Now it is very complicated to make a multi-column structure have rounded corners since you set it separately for different containers. Please see my example:

– You have a 2-column structure and set radius for left corners for the left column on desktop and right corners for the right column.

– On mobile devices it stacks and makes it look not how you need it.

So the only possible way now is to have two separate structures for desktop and mobile views and use media-queries to hide one structure on desktop and other on mobile. But it adds a lot of code, if your email is long it might make it clip in Gmail. There should be more efficient solution. There are two options:

1) Add a common container for all your columns so that you can control their general radius for any device

2) Allow setting different radius parameters for desktop and mobile devices.