Update header and scroll-up button functionalities

Removed unnecessary `background-size` property from the header and updated the scroll-up button to use a service for scrolling.

frontend/src/app/rules/rules.component.html

@@ -1,6 +1,5 @@
 <ng-container>
-  <app-header [current_page]="'rules'" height="460px" background_image="/public/img/backgrounds/trees.jpg"
-              background-size="">
+  <app-header [current_page]="'rules'" height="460px" background_image="/public/img/backgrounds/trees.jpg">
     <div class="title" header-content>
       <h1>Server Rules</h1>
       <h2>We aim to be an inclusive community server where players of all ages can find something to enjoy.</h2>
@@ -256,7 +255,7 @@
         </div>
       </div>
     </section>
-    <a href="#top" id="scroll-up-button">
+    <a (click)="this.scrollService.scrollToTop()" class="scroll-up-button, active">
       <span></span>
       <p style="display: none;">Scroll Down</p>
     </a>