Angular 6 'mat-button-toggle' is not a kno

I've checked those questions:

'mat-toolbar' is not a known element - Angular 5
Jhipster / md-button is not a known element
Template parse errors: 'mat-icon' is not a known element
Meterial 2 md-datepicker-toggle is not a known element
How to bind to model with Angular Material <mat-button-toggle>?

and I've followed this tutorial:

https://material.angular.io/components/button-toggle/overview

and previously I've used Angular Material, but for this it just won't work:

compiler.js:1016 Uncaught Error: Template parse errors: 'mat-button-toggle' is not a known element: 1. If 'mat-button-toggle' is an Angular component, then verify that it is part of this module.

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { TRANSLATION_PROVIDERS } from './translations';
import { TranslateService } from './services/translator.service';
import { AppComponent } from './app.component';
import { MatButtonModule, MatCheckboxModule, MatFormFieldModule, MatInputModule, MatRippleModule, MatDatepickerModule, MatNativeDateModule } from '@angular/material';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import { FormsModule } from '@angular/forms';

import { ReactiveFormsModule } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http';


@NgModule({
  imports: [
    BrowserModule,
    FormsModule,
    MatButtonModule,
    MatCheckboxModule,
    MatFormFieldModule,
    MatInputModule,
    MatRippleModule,
    BrowserAnimationsModule,
    MatDatepickerModule,
  ],
  exports: [
    BrowserModule,
    FormsModule,
    MatButtonModule,
    MatCheckboxModule,
    MatFormFieldModule,
    MatInputModule,
    MatRippleModule,
    BrowserAnimationsModule,
    MatDatepickerModule,
  ],
  declarations: [AppComponent],
  providers: [TRANSLATION_PROVIDERS, TranslateService],
  bootstrap: [AppComponent]
})
export class AppModule { }

(here I am just trying to add those buttons even without real functionality)

....

  <div>
      <mat-button-toggle-group name="fontStyle" aria-label="Font Style">
          <mat-button-toggle value="bold">Bold</mat-button-toggle>
          <mat-button-toggle value="italic">Italic</mat-button-toggle>
          <mat-button-toggle value="underline">Underline</mat-button-toggle>
        </mat-button-toggle-group>
  </div>

...

styles.css

@import '~@angular/material/prebuilt-themes/deeppurple-amber.css';

body { 
  font-family: Roboto, Arial, sans-serif;
  margin: 0;
}

.basic-container {
  padding: 30px;
}

.version-info {
  font-size: 8pt;
  float: right;
}

html, body { height: 100%; }
body { margin: 0; font-family: 'Roboto', sans-serif; }

mat-button-toggle is available as a part of the MatButtonToggleModule So you'll have to import that as well.

Add an import statement for the same in your AppModule:

import {MatButtonToggleModule} from '@angular/material/button-toggle';

And then add it to the imports array as well so that AppModule's templates can understand what mat-button-toggle is.

Also, I'm not really sure why you've exported these modules from your AppModule. We generally export anything from a module if we are planning on importing that module in some other module. But since this is the AppModule, and thus your RootModule, I don't think you'll be importing it in any other module. That might not be the case though.