Add class to body on Angular2
<p>I have three components. These are HomeComponent, SignInComponent and AppComponent. My Home Page (HomeComponent) is showing when the application opened. I clicked the "Sign In" button by signin page opens.I want "signin-page" class to body while opening it.</p>

<p>How can I do it?</p>

<pre><code>// AppComponent
import { Component } from '@angular/core';

@Component({
  moduleId: module.id,
  selector: 'app',
  template: '&lt;router-outlet&gt;&lt;/router-outlet&gt;'
})
export class AppComponent {}

// SignInComponent
import { Component } from '@angular/core';

@Component({
    moduleId: module.id,
    selector: 'signin',
    templateUrl: './signin.component.html',
    styleUrls: ['./signin.component.css']
})
export class SignInComponent {}

// HomeComponent
import { Component } from '@angular/core';

@Component({
    moduleId: module.id,
    selector: 'home',
    templateUrl: './home.component.html'
})
export class HomeComponent { }

// Part of index.html
&lt;body&gt;
&lt;app&gt;
    &lt;div class="spinner"&gt;
        &lt;div class="bounce1"&gt;&lt;/div&gt;
        &lt;div class="bounce2"&gt;&lt;/div&gt;
        &lt;div class="bounce3"&gt;&lt;/div&gt;
    &lt;/div&gt;
&lt;/app&gt;
&lt;/body&gt;
</code></pre>