border radius menu mobile flyout

Greetings,
Is it possible to set the border radius of the flyout mobile menu?

The site is fantasvaimec.it, in the desktop version in flayout (but even if the megamenu is set) I set the border radius and everything is ok, but in the mobile version the large rectangle always opens.

Also, is it possible to center all items in the submenu that pops up?

Using megamenu I can do it with the items but not with any other elements that I insert (images, html), in flyout instead in the mobile version I can’t.

Thank you