Refactor background-position logic in header component

frontend/src/app/header/header.component.html

@@ -1,6 +1,6 @@
 <ng-container>
   <header id="top"
-          [ngStyle]="{ 'background-image': getBackgroundImage(), 'height': height, 'background-position': 'center ' + inverseYPos + 'px' }">
+          [ngStyle]="{ 'background-image': getBackgroundImage(),'height': height, 'background-position': getBackgroundPosition() }">
     <nav id="nav" [ngClass]="active">
       <div class="container">
         <div id="mobile_nav">

frontend/src/app/header/header.component.ts

@@ -41,4 +41,12 @@ export class HeaderComponent {
     }
     return null;
   }
+
+  public getBackgroundPosition() {
+    if (this.current_page === 'home') {
+      return 'center ' + this.inverseYPos + 'px'
+    } else {
+      return '';
+    }
+  }
 }