<div fxLayout="row">
    <div layout="column">
        <div fxFlex="100" fxFlexOffset="1" fxLayoutWrap fxLayoutGap="2rem" class="mat-elevation-z0" *ngIf="postcards != null">
            <mat-card *ngFor="let postcard of postcards let index = index" >
                    <img mat-card-image src="{{postcard.img}}" alt="{{postcard.postcard_id}}" class="postcards" (click)="display_postcard(index)">
            </mat-card>
        </div>
    </div>
</div>

.postcards {
    max-width: 320px;
}