fixup! fix(material/dialog): css structure change

Author: wagnermaciel

src/material/dialog/dialog.ts

@@ -175,7 +175,7 @@ export abstract class _MatDialogBase<C extends _MatDialogContainerBase> implemen
     // the title, contents, and actions are then nested directly under the
     // dialog surface.
     if (!(componentOrTemplateRef instanceof TemplateRef)) {
-      this._appendPanelClass(config);
+      this._appendPanelClass(config, 'mat-mdc-dialog-component-panel');
     }
 
     const cdkRef = this._dialog.open<R, D, T>(componentOrTemplateRef, {
@@ -266,13 +266,14 @@ export abstract class _MatDialogBase<C extends _MatDialogContainerBase> implemen
     }
   }
 
-  private _appendPanelClass(config: MatDialogConfig) {
+  /** Appends the given class name to the panel via the dialog config. */
+  private _appendPanelClass(config: MatDialogConfig, className: string) {
     if (Array.isArray(config.panelClass)) {
-      config.panelClass.push('mat-mdc-dialog-component-panel');
+      config.panelClass.push(className);
     } else if (typeof config.panelClass === 'string') {
-      config.panelClass = [config.panelClass, 'mat-mdc-dialog-component-panel'];
+      config.panelClass = [config.panelClass, className];
     } else {
-      config.panelClass = 'mat-mdc-dialog-component-panel';
+      config.panelClass = className;
     }
   }
 }