Conditional Styling of an Angular component

You can use style.propertyName to set any conditional style property.

<div class="col-md-3 d-flex justify-content-center align-items-center" [style.background]="someFunction()">

ng-style is the syntax for AngularJS. For Angular 2+, use [ngStyle]="" syntax. (see documentation)

<div class="col-md-3 d-flex justify-content-center align-items-center" 
     [ngStyle]="{'background-color': (vars.state=='Signup') ? '#73c7af' : '#ffffff'}">