How to center align card in angular material 4?

I have created a sample angular 4 application with angular material. I'm trying to center the card in the view. But its not working.Below is the code

app.component.html

<!--The content below is only a placeholder and can be replaced.-->
<router-outlet></router-outlet>

login.component.html

<div  ng-cloak=""  layout-fill layout="column" style="background:green" layout-align="center">
    <div flex="50" layout="row" layout-align="center">
      <md-card flex="50"></md-card>
    </div>
</div>

login.component.ts

import { Component, OnInit } from '@angular/core';
import { MdCardModule,MdInputModule } from '@angular/material';

@Component({
  selector: 'app-login',
  templateUrl: './login.component.html',
  styleUrls: ['./login.component.css']
})
export class LoginComponent implements OnInit {

  constructor() { }

  ngOnInit() {
  }

}