adding an angular animation to a host element

The square brackets are not necessary with @HostBinding()

@HostBinding('@slideIn') get slideIn() {

There are two decorators @HostBinding() and @HostListener() therefore the distinction between () and [] isn't necessary, while it is when host: [...] is used.

I'm writing this answer because I struggled a little bit with the syntax and I like examples for dummies, but Günter's answer is correct.

What I had to do:

    @Component({
        selector: 'app-sidenav',
        templateUrl: './sidenav.component.html',
        styleUrls: ['./sidenav.component.scss'],
        animations: [
            trigger('toggleDrawer', [
                state('closed', style({
                    transform: 'translateX(0)',
                    'box-shadow': '0px 3px 6px 1px rgba(0, 0, 0, 0.6)'
                })),
                state('opened', style({
                    transform: 'translateX(80vw)'
                })),
                transition('closed <=> opened', animate(300))
            ])
        ]
    })
    export class SidenavComponent implements OnInit {

        private state: 'opened' | 'closed' = 'closed';

        // binds the animation to the host component
        @HostBinding('@toggleDrawer') get getToggleDrawer(): string {
            return this.state === 'closed' ? 'opened' : 'closed';
        }

        constructor() { }

        ngOnInit(): void {
        }

        // toggle drawer
        toggle(): void {
            this.state = this.state === 'closed' ? 'opened' : 'closed';
        }

        // opens drawer
        open(): void {
            this.state = 'opened';
        }

        // closes drawer
        close(): void {
            this.state = 'closed';
        }

    }