Widget _buildTextField() {
  final maxLines = 5;

  return Container(
    margin: EdgeInsets.all(12),
    height: maxLines * 24.0,
    child: TextField(
      maxLines: maxLines,
      decoration: InputDecoration(
        hintText: "Enter a message",
        fillColor: Colors.grey[300],
        filled: true,
      ),
    ),
  );
}