:::
6-1 開權限
6-2 取得螢幕大小+圓角矩形
Size size = MediaQuery.of(context).size;
用法：
Container(
width: size.width * 0.8,
height: 300.0,
decoration: BoxDecoration(
color: Color(0xff1f1f1f),
borderRadius: BorderRadius.circular(5.0)
),
),
http://laomengit.com/flutter/widgets/MediaQuery.html#mediaquery
