Update 2/11/19

The file size upload limit is 10mb for both Website>Page>Files and Website>Custom theme>Files. If you'll be uploading files greater than 10mb in size, you may want to consider uploading content on an external host like Dropbox.

The file size upload limit is 10mb when uploading files into an individual page under Website>Page>Files. On the other hand, under the page theme you can host a file up to 20mb in size given that it is uploaded to Website>Custom theme>Files. If you'll be uploading more robust files greater than 20mb in size, you may want to consider uploading content on an external host.