step background-image only if its the first step of the line

src/app/pieces/step/step.component.html

@@ -21,7 +21,7 @@
     <div class="piece-form">
         <div class="piece-form-title">Étape {{index+1}}</div>
         <mat-icon class="piece-form-comment" fontIcon="comment" *ngIf="step.comments.length > 0"></mat-icon>
-        <textarea [(ngModel)]="step.description"></textarea>
+        <textarea [(ngModel)]="step.description" [style.background-image]="index == FirstStepIndex() ? urlIcon : ''"></textarea>
         <div class="piece-form-duration">
             <label for="duration">Durée</label>
             <input name="duration" type="number" [(ngModel)]="step.duration" (input)="durationChange()"/>

src/app/pieces/step/step.component.scss

@@ -97,7 +97,6 @@
             border-radius: 10px;
             border: none;
             resize: none;
-            background-image: url("../../../assets/background-images/step.png");
             background-position: center;
             background-repeat: no-repeat;
             background-size: 100px;

src/app/pieces/step/step.component.ts

@@ -22,6 +22,7 @@ export class StepComponent implements OnInit {
 
   displayMenu: string = 'hide';
   pieceWidth: number = 400;
+  urlIcon: string = 'url("../../../assets/background-images/step.png")';
 
   constructor(protected pieceDetailsService: PieceDetailsService, public dialog: MatDialog, protected tooltipService: TooltipService) { }
 
@@ -102,4 +103,13 @@ export class StepComponent implements OnInit {
     this.displayMenu = 'hide';
     this.mission.equalizeLengths();
   }
+
+  FirstStepIndex(): number {
+    for(let i = 0; i < this.parent.chronologie.length; i++) {
+      if (this.parent.chronologie[i] instanceof Step) {
+        return i;
+      }
+    }
+    return 0;
+  }
 }
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