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<div [style.background-color]="style1 ? 'red' : (style2 ? 'blue' : null)">
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<div [ngStyle]="{'background-color': style1 ? 'red' : (style2 ? 'blue' : null) }">
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<div [ngClass]="{'class1': true, 'class2': false}"></div> <!--passed as an object-->