child.component.html
<button (click)="buttonClicked()"></button>
child.component.ts
@Output() clicked=new EventEmitter();
buttonClicked(){
this.clicked.emit();
}
parent.component.html
<child-component (clicked)="childClicked()"></child-component>
parent.component.ts
childCliked(){
//do anything that could affect the html in the parent
}