ng-bootstrap not working in angular 4

I am new with angular 4, I am trying to configure bootstrap. I installed ng-bootstrap:

https://ng-bootstrap.github.io/#/getting-started

I did all like on the page, but I don't see the bootstrap on my page. Here is my code:

src/app/app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppComponent } from './app.component';
import { FormsModule } from '@angular/forms';
import {NgbModule} from '@ng-bootstrap/ng-bootstrap';

@NgModule({
  declarations: [
    AppComponent
  ],
imports: [
   BrowserModule,
   FormsModule,  // add  this
   NgbModule.forRoot()
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule { }

src/app/app.component.html

<div class="container">

<h1 class="text-primary">{{title}} </h1>

<h2 class="text-primary">My Heroes</h2>
<ul class="heroes">
  <li *ngFor="let hero of heroes"
    [class.selected]="hero === selectedHero"
    (click)="onSelect(hero)">
    <span class="badge">{{hero.id}}</span> {{hero.name}}
   </li>
</ul>

<div class="alert alert-success" role="alert">
 <strong>Well done!</strong> You successfully read this important alert 
   message.
</div>

<div *ngIf="selectedHero">
  <h2>{{selectedHero.name}} details!</h2>
<div><label>id: </label>{{selectedHero.id}}</div>
<div>
  <label>name: </label>
  <input [(ngModel)]="selectedHero.name" placeholder="name"/>
</div>

I tried also some code in the index.html, but it does not work,

for this line I am expecting to see some color:

<h1 class="text-primary">{{title}} </h1>

I don't find any reference of bootstrap when I check the header of the html. Any help, please? Thanks