Use separate file for plugin placeholder component

client/src/app/shared/shared-main/plugins/plugin-placeholder.component.scss

@@ -0,0 +1,3 @@
+div {
+  height: 100%;
+}

client/src/app/shared/shared-main/plugins/plugin-placeholder.component.ts

@@ -4,7 +4,7 @@ import { PluginElementPlaceholder } from '@shared/models'
 @Component({
   selector: 'my-plugin-placeholder',
   template: '<div [id]="getId()"></div>',
-  styles: [ 'div { height: 100%; }' ]
+  styleUrls: [ './plugin-placeholder.component.scss' ]
 })
 
 export class PluginPlaceholderComponent {