Make the ThemedCssFolderUrl property of the Web object available in the CSOM
You cannot currently load or set the ThemedCssFolderUrl property of the Web object in CSOM. After applying a theme (for example, using the sample PnP code), returning to the app from the newly-themed site shows that the SP.UI chrome control cannot find what it needs to properly display. We need a way to ensure that a new theme that is deployed from the app can set this value so that when returning to the app afterwards the chrome control can continue to display properly.
We released this property as part of the November 2016 SharePoint Online CSOM NuGet package release. Thanks for your input and hopefully you’ll find the enhancement useful. See more details on the latest release from https://dev.office.com/blogs/new-sharepoint-csom-version-released-for-Office-365-november-2016