In addition to all provided values of position (see #13) should there be top-stretch, center-stretch, or bottom-stretch values available to use when the developer wants to fit the toast to the entire width of the screen? Or should this stretching be done manually via CSS? Through some property other than position?

This stretching is the popular way of handling toasts on mobile, should the stretch be applied to toasts automatically when mobile platform is detected, or is that an option that should be left to the developer?