Added new kb article fix-forest-theme-not-working-telerik-ui-ajax (#525)

Co-authored-by: KB Bot <[email protected]>

Author: github-actions[bot]

knowledge-base/fix-forest-theme-not-working-telerik-ui-ajax.md

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+---
+title: How to Fix Forest Theme Not Working in Telerik UI for ASP.NET AJAX
+description: Learn how to fix the issue where the Forest theme is not working in Telerik UI for ASP.NET AJAX.
+type: how-to
+page_title: Fix Forest Theme Not Working | Telerik UI for ASP.NET AJAX
+slug: fix-forest-theme-not-working-telerik-ui-ajax
+tags: theme, Telerik UI, ASP.NET AJAX, Forest, fix
+res_type: kb
+---
+## Environment
+| Product         | Telerik UI for ASP.NET AJAX |
+|-----------------|-------------------------------|
+| Version         | all           |
+
+## Description
+I upgraded Telerik UI for ASP.NET AJAX, but the Forest theme is no longer working. It was working fine in previous versions. I would like to know if it has been replaced or how to fix this issue.
+
+## Solution
+The Forest skin in Telerik UI for ASP.NET AJAX is discontinued and is no longer available. It was announced as obsolete in the blog post [6 Telerik ASP.NET AJAX Skins Going Obsolete](https://www.telerik.com/blogs/6-telerik-asp.net-ajax-skins-going-obsolete). 
+
+To resolve this issue, there are two approaches:
+
+Option 1: Create a Custom Theme
+1. Use the [ThemeBuilder app](https://themebuilder.telerik.com/aspnet-ajax) to create your own custom theme.
+2. Follow the instructions [here](https://docs.telerik.com/devtools/aspnet-ajax/controls/themebuilder/how-to/create-custom-theme) to create a custom theme with the ThemeBuilder.
+3. Download the custom theme and apply it to your page with the Telerik controls. Instructions can be found [here](https://docs.telerik.com/devtools/aspnet-ajax/controls/themebuilder/how-to/download-apply-theme). Note that the ThemeBuilder produces skins for the Lightweight rendering, so make sure to set the RenderMode properties of the Telerik controls to Lightweight.
+
+Option 2: Choose an Available Theme
+1. Choose one of the available 21 themes instead of the Forest theme.
+2. Set the Skin properties of the Telerik controls to the chosen theme. For example, you can set it to "Default" which is also gray colored.
+3. Test your page again with the new theme.
+
+Note: The ThemeBuilder app is only available for the Lightweight rendering mode.
+
+