https://stackoverflow.com/questions/34323480/in-angular-how-do-you-determine-the-active-route
<!-- if multiple classes need to be inserted -->
<a [routerLink]="['/home']" [routerLinkActive]="['is-active']">Home</a>
<a [routerLink]="['/home']" [routerLinkActive]="'is-active'">Home</a>
<a [routerLink]="['/home']" routerLinkActive="is-active">Home</a>https://stackoverflow.com/questions/35269179/angular-conditional-class-with-ngclass
[class.my_class] = "step === 'step1'"
[ngClass]="{'my_class': step === 'step1'}"
[ngClass]="{'my_class': step === 'step1', 'my_class2' : step === 'step2' }"
[ngClass]="{1 : 'my_class1', 2 : 'my_class2', 3 : 'my_class4'}[step]"
[ngClass]="step == 'step1' ? 'my_class1' : 'my_class2'"