Fixes to horizontal menu logic. Now supports two levels of menu items.

Oqtane.Client/Themes/Controls/MenuItemsBase.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+using System.Linq;
+
+using Microsoft.AspNetCore.Components;
+
+using Oqtane.Models;
+using Oqtane.UI;
+
+namespace Oqtane.Themes.Controls
+{
+    public abstract class MenuItemsBase : MenuBase
+    {
+        [Parameter()]
+        public Page ParentPage { get; set; }
+
+        [Parameter()]
+        public IEnumerable<Page> Pages { get; set; }
+
+        protected IEnumerable<Page> GetChildPages()
+        {
+            return Pages
+                .Where(e => e.ParentId == ParentPage?.PageId)
+                .OrderBy(e => e.Order)
+                .AsEnumerable();
+        }
+    }
+}