Answers for "how to change button color in flutter using style"

textbutton background color flutter

// first way (most upvoted)
TextButton(
    child: Text('test'),
    style: ButtonStyle(backgroundColor: MaterialStateProperty.all(Colors.red)),
    onPressed: () {},
),

// second way 
TextButton(
  child: Text('Example'),
  onPressed: () {},
  style: TextButton.styleFrom(backgroundcolor: Colors.red),
)

// third way
TextButton(
  onPressed: () {},
  child: Container(
    padding: EdgeInsets.fromLTRB(30, 10, 30, 10),
    color: Colors.red,
    child: Text(""),
  ),
)

Flutter Elevated button color

ElevatedButton(
            child: Text('Button'),
            onPressed: () {},
            style: ButtonStyle(
                backgroundColor: MaterialStateProperty.all(Colors.red),
                padding: MaterialStateProperty.all(EdgeInsets.all(50)),
                textStyle: MaterialStateProperty.all(TextStyle(fontSize: 30))),
),