Just wrap you column with Center for cross axis alignment center to work.

 Center(
  child: Column(
    crossAxisAlignment: CrossAxisAlignment.center,
    children: [
      TextField(
        controller: _emailController,
        decoration: const InputDecoration(
          labelText: 'Email',
        ),
      ),
      TextField(
        controller: _passwordController,
        decoration: const InputDecoration(
          labelText: 'Password',
        ),
        obscureText: true,
      ),
    ],
  ),
);

Similarly, wrap row with Center for mainAxisAlignment: MainAxisAlignment.center to work:

Center(
  child: Row(
    mainAxisAlignment: MainAxisAlignment.center,
    children: [
      
    ],
  ),
)

screenshot: