Dropdown menu with Bootstrap in Angular

I'm practising Angular. Here is my practice project on Stackblitz

I followed the Angular tutorial . Everything is great, no problem at all.

Then, I tried this tutorial to add a dropdown menu

• I created a new component "dropdown-basic"
• Copied the dropdown-basic.html file over
• Copied the inhalt of Style tag in index.html to app.component.css
• Modified my app.module.ts according to the module.ts file in tutorial
• Added the dropdown-basic component to app.component.html

But then, the dropdown menu doesn't work. the list items are always shown. And, the buttons don't hide or show the items. I would like some help please, thank you very much.

My screenshot

dropdown-basic.component.html

<div class="row">
  <div class="col">
    <div ngbDropdown class="d-inline-block">
      <button class="btn btn-outline-primary" id="dropdownBasic1" ngbDropdownToggle>Toggle dropdown</button>
      <div ngbDropdownMenu aria-labelledby="dropdownBasic1">
        <button ngbDropdownItem>Action - 1</button>
        <button ngbDropdownItem>Another Action</button>
        <button ngbDropdownItem>Something else is here</button>
      </div>
    </div>
  </div>

  <div class="col text-right">
    <div ngbDropdown placement="top-right" class="d-inline-block">
      <button class="btn btn-outline-primary" id="dropdownBasic2" ngbDropdownToggle>Toggle dropup</button>
      <div ngbDropdownMenu aria-labelledby="dropdownBasic2">
        <button ngbDropdownItem>Action - 1</button>
        <button ngbDropdownItem>Another Action</button>
        <button ngbDropdownItem>Something else is here</button>
      </div>
    </div>
  </div>
</div>

dropdown-basic.component.ts

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

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

  constructor() { }

  ngOnInit() {
  }

}

app.component.css

p {
  font-family: Lato;
}

/* Datepicker popup icon */

button.calendar, button.calendar:active {
  width: 2.75rem;
  background-image: url('data:image/png;base64,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') !important;
  background-repeat: no-repeat;
  background-size: 23px;
  background-position: center;
}

/* Sortable table demo */

th[sortable] {
  cursor: pointer;
  user-select: none;
  -webkit-user-select: none;
}

th[sortable].desc:before, th[sortable].asc:before {
  content: '';
  display: block;
  background: url('data:image/png;base64,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') no-repeat;
  background-size: 22px;
  width: 22px;
  height: 22px;
  float: left;
  margin-left: -22px;
}

th[sortable].desc:before {
  transform: rotate(180deg);
  -ms-transform: rotate(180deg);
}

/* Filtering table demo */
ngbd-table-filtering span.ngb-highlight {
  background-color: yellow;
}

/* Complete table demo */
ngbd-table-complete span.ngb-highlight {
  background-color: yellow;
}

ngb-carousel .picsum-img-wrapper {
  position: relative;
  height: 0;
  padding-top: 55%; /* Keep ratio for 900x500 images */
}

ngb-carousel .picsum-img-wrapper>img {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
}

app.module.ts

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { NgbModule } from '@ng-bootstrap/ng-bootstrap';
import { RouterModule } from '@angular/router';
import { ReactiveFormsModule } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http'; /** The Angular HTTP client (HttpClient) is a built-in way to fetch data from external APIs and provide them to your application as a stream. */

import { AppComponent } from './app.component';
import { TopBarComponent } from './top-bar/top-bar.component';
import { ProductListComponent } from './product-list/product-list.component';
import { ProductAlertsComponent } from './product-alerts/product-alerts.component';
import { ProductDetailsComponent } from './product-details/product-details.component';
import { CartService } from './cart.service';
import { CartComponent } from './cart/cart.component';
import { ShippingComponent } from './shipping/shipping.component';
import { DropdownBasicComponent } from './dropdown-basic/dropdown-basic.component';

@NgModule({
  imports: [
    BrowserModule,
    HttpClientModule, /** use the HTTP client to retrieve shipping prices from an external file */
    ReactiveFormsModule,
    NgbModule,
    RouterModule.forRoot([ /** add routing for components */
      { path: '', component: ProductListComponent },
      { path: 'products/:productId', component: ProductDetailsComponent },
      { path: 'cart', component: CartComponent },
      { path: 'shipping', component: ShippingComponent },
    ])
  ],
  declarations: [
    AppComponent,
    TopBarComponent,
    ProductListComponent,
    ProductAlertsComponent,
    ProductDetailsComponent,
    CartComponent,
    ShippingComponent,
    DropdownBasicComponent
  ],
  bootstrap: [ AppComponent ],
  providers: [ CartService ],
  exports: [ AppComponent ]
})
export class AppModule { }

app.component.html

<app-top-bar></app-top-bar>

<div class="container">
  <router-outlet></router-outlet>
</div>

<div class="container-fluid">

    <hr>

    <p>
      This is a demo example forked from the <strong>ng-bootstrap</strong> project: Angular powered Bootstrap.
      Visit <a href="https://ng-bootstrap.github.io/" target="_blank">https://ng-bootstrap.github.io</a> for more
      widgets and demos.
    </p>

    <hr>
    <app-dropdown-basic></app-dropdown-basic>
</div>