Can I use ngClass on the ng-template?

You can’t put element attributes on an <ng-template> since it doesn’t map to an actual DOM element. The best you can do is this:

<ng-template contextMenuItem (execute)="doSomething($event.item)">
  <div [ngClass]="{'first': true}"></div>
</ng-template>

If all you want to do is write a css rule for the first context menu item, you can do that without a class.

.ngx-contextmenu li:first-child {
  background-color:red;
}

In you css file => .loading { margin: 10% 0 0 50%; }

In the HTML file =>

<ng-template #loading>
  <div class="loading">
    <img  src="/images/spinner.gif" />
  </div>
</ng-template>

OR In you css file => .loading { margin: 10% 0 0 50%; }

In the HTML file =>

<ng-template #loading>
  <div [class.loading]="product.loading">
    <img  src="/images/spinner.gif" />
  </div>
</ng-template>

In the component file .ts

/*Declare property*/
product : Product;

/*Initialize property*/
ngOnInit() { 
this.product = {"name" : "iphone",  "loading" : true};
}

In the Interface file declare custom type property

export interface Product {
  name : string;
  loading : boolean; 
}