Is this currently an existing feature request?
no
Wishlist item
Ability to control the radius, corners of iFrame box, and maps natively or with CSS.
What current pain point are you facing?
We are unable to make corners of HTML boxes and Maps
Do you have a current workaround that you’re using?
Adding vector art to each corner
Describe the feature you need and how it would work. (Bonus points for mockups 
)
How will this impact you?
Give more customization for these items.