怎样使用Angular5为组件标签添加样式class

@Component({
 selector : 'myComponent',
 host : {
  '[style.color]' : "'red'", 
  '[style.background-color]' : 'backgroundColor'
 }
})
class MyComponent {
 backgroundColor: string;
 constructor() {
  this.backgroundColor = 'blue';
 }
}

@Component({
 selector : 'myComponent',
 host : {
  '[class.myclass]' : 'showMyClass'
 }
})
class MyComponent {
 showMyClass = false;
 constructor() {
 }

 toggleMyClass() {
  this.showMyClass = !this.showMyClass;
 }
}

@Component({
 selector : 'myComponent',
 styles : [`
  :host {
   color: red;
   background-color: blue;
  }
 `]
})
class MyComponent {}