Theme的canvasColor屬性可以修改下拉欄背景色

List<String> _demoList = ['one', 'two'];
// 外層Theme的canvasColor屬性可以修改下拉欄背景色
Theme(
  data: Theme.of(context).copyWith(
    canvasColor: Color.fromRGBO(27, 29, 67, 1.00),
  ),
  // DropdownButtonHideUnderline 沒有下劃線的下拉欄
  child: DropdownButtonHideUnderline(
      child: DropdownButton(
          style: TextStyle(color: Color.fromRGBO(0, 255, 255, 1.00),),
          items: _demoList.map((value) {
              return DropdownMenuItem(
                  child: Text(value),
                  value: value,
              );
          }).toList(),
          value: _demoList,
          onChanged: (String value) {
              setState(() {
                  _demoList = value;
              });
          },
  )))