您可以尝试将Container Package 在Align Widget中，并将对齐方式设置为bottomCenter

Align(
                alignment: Alignment.bottomCenter,
                child: Container(
                    padding: EdgeInsets.all(10),
                    width: double.infinity,
                    margin: EdgeInsets.only(top: 60),
                    color: Colors.white,
                    child: Text(category.title)),
              )

只是不要使用您的Stack小部件并将其更改为Column

class CategoryItem extends StatelessWidget {
  final Category category;
  const CategoryItem({super.key, required this.category});

  @override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;
    return Container(
      padding: EdgeInsets.only(top: 20),
      decoration: BoxDecoration(
        color: category.backColor,
        borderRadius: BorderRadius.only(
          topLeft: Radius.circular(10), 
          topRight: Radius.circular(10)
        )
      ),
      child: Column(
        children: [
          Image.asset(
            category.image,
            height: 80,
            width: 80,
            alignment: Alignment.topCenter,
          ),
          Container(
            padding: EdgeInsets.all(10),
            width: double.infinity,
            margin: EdgeInsets.only(top: 60),
            color: Colors.white,
            child: Text(category.title)
            )
        ]
      ),
    );
  }
}

现在，您小部件设计应该可以按照您的要求工作了