I create this button with complete all of your need, having the box shadow, italic login, responsive design base on device width.
GestureDetector(
behavior: HitTestBehavior.opaque,
onTap: () {},
child: Container(
width: MediaQuery.of(context).size.width * 0.4,
height: MediaQuery.of(context).size.height * 0.05,
decoration: BoxDecoration(
color: const Color(0xff92fcd1),
border: Border.all(color: Colors.black),
borderRadius: BorderRadius.circular(100),
boxShadow: [
BoxShadow(
color: Colors.black.withOpacity(0.7),
spreadRadius: 2,
offset:
const Offset(2, 2), // changes position of shadow
),
],
),
child: const Center(
child: Text("Login",
style: TextStyle(
fontStyle: FontStyle.italic, color: Colors.black)),
),
),
)
and here is the result