Container with 3 borders and radiuses

Question

I'm looking for the way to create rounded container with only topLeft and topRight radiuses and without bottom border. Here is what I tried:

                      Container(
                        decoration: BoxDecoration(
                          border: Border(
                            left: BorderSide(
                              color: AppColors.lightPurple2,
                            ),
                            right: BorderSide(
                              color: AppColors.lightPurple2,
                            ),
                            top: BorderSide(
                              color: AppColors.lightPurple2,
                            ),
                          ),
                          // border: Border.all(
                          //   color: AppColors.lightPurple2,
                          // ),
                          borderRadius: BorderRadius.only(
                            topLeft: Radius.circular(Rad.sm),
                            topRight: Radius.circular(Rad.sm),
                          ),
                        ),

But this code doesn't work

======== Exception caught by rendering library =====================================================
The following assertion was thrown during paint():
A borderRadius can only be given for a uniform Border.

The following is not uniform:
BorderSide.color
BorderSide.width
BorderSide.style

However if I use Border.all() it works good but I need to remove bottom border somehow. If I remove borderRadius it draw 3 border but without radiuses.

So is there a way to use both options?

What I want to get eventually:

Answer 1

You can use shadow and achieve the same result

 Container(
                height: 300,
                width: 300,
                decoration: BoxDecoration(
                    borderRadius:
                        BorderRadius.vertical(top: Radius.circular(10)),
                    color: Colors.white,
                    boxShadow: [
                      BoxShadow(
                          color: Colors.purple,
                          offset: Offset(2, -2),
                          spreadRadius: 0,
                          blurRadius: 0),
                      BoxShadow(
                          color: Colors.purple,
                          offset: Offset(-2, -2),
                          spreadRadius: 0,
                          blurRadius: 0)
                    ]))