ใจ...หยุด 24 น. #1

Here’s what I added to a Code Block:

 <iframe id="db" src="https://dl.dropboxusercontent.com/s/5jdfd8besbbfhn6/embedded%20db%20test.txt"></iframe> 

You need to change the Dropbox domain from:
https://www.dropbox.com/
to:
https://dl.dropboxusercontent.com/ as in the example above.