Add or remove css class
<div [ngClass]="{className: expresion }">
Sarasa
</div>
<!--The expresion is evaluated and if is true the class will be add to the element -->
<div [ngClass]="{className: true }">
Sarasa
</div>
<div [ngClass]="{className: 1 + 1 }">
Sarasa
</div>
<div [ngClass]="{className: propertyThatIsTRue }">
Sarasa
</div>
<div [ngClass]="{'red': 1+1 != 0}">
Sarasa
</div>
Sarasa
</div>