(fix): css class should be modifier

src/app/modules/pro/channel/channel.component.scss

@@ -14,7 +14,7 @@ m-pro--channel {
   background-blend-mode: overlay;
   background-color: var(--m-pro--more-transparent-background-color) !important;
 
-  &.m-pro-channel__plainBackground {
+  &.m-pro-channel--plainBackground {
     background-blend-mode: initial;
     background-color: var(--m-pro--plain-background-color) !important;
   }

src/app/modules/pro/channel/channel.component.ts

@@ -148,7 +148,7 @@ export class ProChannelComponent implements OnInit, AfterViewInit, OnDestroy {
     ];
 
     if (!this.channel || !this.channel.pro_settings.background_image) {
-      classes.push('m-pro-channel__plainBackground');
+      classes.push('m-pro-channel--plainBackground');
     }
 
     return classes.join(' ');