Step 1: upload your banner and open it in Ad Editor
Step 2: Go to "Elements" section and click on "20%OFF" (discount code widget) in Ad Editor
That is it - now you can configure colors and other settings:
How will it work?
If you use a discount code element in a banner, then after visitor will close this banner, he will still be able to see the discount code in a small Ribbon in the bottom of site.
In case you also use a countdown timer, then after closing banner, small Ribbon will show both - discount code and also time left to use it. Example below:
And here you can see, how the Ribbon would look like with and without countdown timer: