How to Add HTML (custom widgets) to a page or post:
1. Login to your WordPress dashboard.
2. In the navigation menu click the Pages or Posts link, depending which one you want to add the widget to. For the purpose of this article we clicked Posts.
3. Now, click the page or post that you want to edit.
4. Click the plus tab in the upper left to show the block options.
Search for the HTML block. (Do not use the Embed block)
5. Copy and paste the widget code (from: https://designfiles.co/settings/widget) into the HMTL block.
6. Click Update to save your changes. You will now see the widget on the front end of the page you just edited.