Updated to public preview.15 version of the package, fixed assembly definition references

Assets/UI Toolkit/UnityThemes/UnityDefaultRuntimeTheme.tss

-@import url("unity-theme://default")
+@import url("unity-theme://default");

Packages/manifest.json

     "com.unity.ide.rider": "3.0.7",
     "com.unity.ide.visualstudio": "2.0.9",
     "com.unity.ide.vscode": "1.2.3",
-    "com.unity.render-pipelines.lightweight": "10.1.0",
+    "com.unity.render-pipelines.lightweight": "10.5.0",
-    "com.unity.textcore": "file:../../../last_compatible/ModuleOverrides/com.unity.textcore",
-    "com.unity.ui": "file:../../../last_compatible/ModuleOverrides/com.unity.ui",
+    "com.unity.ui": "1.0.0-preview.15",
+    "com.unity.ui.builder": "1.0.0-preview.15",
     "com.unity.vectorgraphics": "2.0.0-preview.12",
     "com.unity.modules.ai": "1.0.0",
     "com.unity.modules.androidjni": "1.0.0",

Packages/packages-lock.json

       "url": "https://packages.unity.com"
     },
     "com.unity.render-pipelines.lightweight": {
-      "version": "10.1.0",
+      "version": "10.5.0",
-        "com.unity.render-pipelines.universal": "10.1.0",
+        "com.unity.render-pipelines.universal": "10.5.0",
         "com.unity.postprocessing": "2.1.7"
       },
       "url": "https://packages.unity.com"
       "url": "https://packages.unity.com"
     },
     "com.unity.test-framework": {
-      "version": "1.1.24",
+      "version": "1.1.27",
       "depth": 1,
       "source": "registry",
       "dependencies": {
       "url": "https://packages.unity.com"
     },
     "com.unity.textcore": {
-      "version": "file:../../../last_compatible/ModuleOverrides/com.unity.textcore",
-      "depth": 0,
-      "source": "local",
-      "dependencies": {}
+      "version": "1.0.0-preview.3",
+      "depth": 1,
+      "source": "registry",
+      "dependencies": {},
+      "url": "https://packages.unity.com"
     },
     "com.unity.textmeshpro": {
       "version": "3.0.6",
       }
     },
     "com.unity.ui": {
-      "version": "file:../../../last_compatible/ModuleOverrides/com.unity.ui",
+      "version": "1.0.0-preview.15",
-      "source": "local",
+      "source": "registry",
-        "com.unity.modules.uielementsnative": "1.0.0"
-      }
+        "com.unity.modules.uielementsnative": "1.0.0",
+        "com.unity.textcore": "1.0.0-preview.3"
+      },
+      "url": "https://packages.unity.com"
+    },
+    "com.unity.ui.builder": {
+      "version": "1.0.0-preview.15",
+      "depth": 0,
+      "source": "registry",
+      "dependencies": {},
+      "url": "https://packages.unity.com"
     },
     "com.unity.vectorgraphics": {
       "version": "2.0.0-preview.12",

ProjectSettings/ProjectVersion.txt

-m_EditorVersion: 2020.3.10f1
-m_EditorVersionWithRevision: 2020.3.10f1 (297d780c91bc)
+m_EditorVersion: 2020.3.14f1
+m_EditorVersionWithRevision: 2020.3.14f1 (d0d1bb862f9d)

Assets/UITKRuntimeDemo.asmdef

+{
+    "name": "UITKRuntimeDemo",
+    "rootNamespace": "",
+    "references": [
+        "UnityEngine.UIElementsModule",
+        "Unity.Addressables",
+        "Unity.ResourceManager",
+        "Cinemachine",
+        "Unity.Timeline",
+        "NavMeshComponents"
+    ],
+    "includePlatforms": [],
+    "excludePlatforms": [],
+    "allowUnsafeCode": false,
+    "overrideReferences": false,
+    "precompiledReferences": [],
+    "autoReferenced": false,
+    "defineConstraints": [],
+    "versionDefines": [],
+    "noEngineReferences": false
+}

Assets/UITKRuntimeDemo.asmdef.meta

+fileFormatVersion: 2
+guid: 0707d8fe56492483ca06ec601d312298
+AssemblyDefinitionImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: