NG2-If-else-ngClass-apply

component1.html
-----------------
<div [ngClass]="{'n-dropdown-menu--active': isActive, 'n-dropdown-menu': true}">

<a (click)="isActive = !isActive">Click</a>
</div>

component1.component.ts
-----------------------
import {component} from 'angular@/core';

@componet{

}
export class classname{

isActive =false;

}

component1.css
--------------
n-dropdown-menu--active{

background : red;
}
n-dropdown-menu{

background: Green;
}

By default the dropdown background color is green. Once click,
 it will be toogle the color as red and green