隠すWidget

Container(
  constraints: BoxConstraints.tightFor(width: double.infinity, height: double.infinity),
  child: Row(
    children: [
      // Your widgets here
    ],
  ),
  decoration: BoxDecoration(
    border: Border.all(width: 1.0, color: Colors.black),
  ),
  clipBehavior: Clip.hardEdge,
)