child: Padding(
            padding: const EdgeInsets.all(20.0),
            child: Row(
              children: [
                Expanded(
                  flex: 2,
                  child: OutlinedButton(
                    onPressed: () {},
                    child: Text(
                      "确认注销",
                      style: TextStyle(color: Colors.grey),
                    ),
                    style: OutlinedButton.styleFrom(
                      shape: RoundedRectangleBorder(
                        borderRadius: BorderRadius.circular(18.0),
                      ),
                      side: BorderSide(width: 1, color: Colors.grey),
                    ),
                  ),
                ),
                SizedBox(
                  width: 10,
                ),
                Expanded(
                  flex: 3,
                  child: MaterialButton(
                    color: widget.color,
                    onPressed: () {},
                    child: Text(
                      "我再想想",
                      style: TextStyle(color: Colors.white),
                    ),
                    shape: RoundedRectangleBorder(
                      borderRadius: BorderRadius.circular(18.0),
                    ),
                  ),
                ),
              ],
            ),
          )

Expanded设置 ​​flex​​ 即可

Flutter 实现百分比布局 OutlinedButton 与MaterialButton设置圆角_ide