[player] Replace flex layout module in PageScrollButtonComponent

projects/player/src/app/components/page-scroll-button/page-scroll-button.component.html

 <ng-content></ng-content>
-<div fxLayout="column" fxLayoutAlign="center center"
-     class="scroll-button-container">
+<div class="fx-column-center-center scroll-button-container">
   <button *ngIf="isVisible.value"
           mat-fab
           class="scroll-button"

projects/player/src/app/components/page-scroll-button/page-scroll-button.component.scss

@@ -16,3 +16,11 @@
   pointer-events: none;
   z-index: 100;
 }
+
+.fx-column-center-center {
+  box-sizing: border-box;
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  align-items: center;
+}