Paste the code to your Publii website’s HTML field.
Next, go to your Publii plugin editor and find the HTML field. It is most likely in the form of an HTML/Code widget or module which you can find on the Publii’s editor. Add it to your page, and paste the Corner Button Embed Code you’ve copied before to the HTML field.
Save and update, and that’s it, you should have Common Ninja’s Corner Button website on your Publii plugin.