feat: optimize theme images

docs/app/pages/home/main-info-section/main-info-section.component.ts

@@ -34,7 +34,7 @@ export class MainInfoSectionComponent implements OnDestroy {
 
   public get imageUrl(): string {
     return this.forMaterialTheme !== false
-      ? 'assets/img/ngx-admin-material.png'
+      ? 'assets/img/ngx-admin-material.jpg'
       : 'assets/img/ngx-admin.png';
   }
 

src/app/themes-screen/starter.component.html

@@ -38,7 +38,7 @@
         <nb-card (click)="navigate(theme.value)">
           <nb-card-header>{{theme.name}}</nb-card-header>
           <nb-card-body>
-            <img src="assets/images/{{theme.value}}-theme.png"
+            <img src="assets/images/{{theme.value}}-theme.jpg"
                  class="theme-preview"
                  alt="{{theme.name}} Theme"/>
           </nb-card-body>