When configuring your Thrive Ultimatum campaigns, you can set the countdown timer design to display as a ribbon.
Below you can see a video that will walk you through the entire process of displaying a ribbon countdown timer on your website:
Don't forget to make sure that the "Top Ribbon" is set to be displayed, by clicking this checkbox in the "Timeline Event Settings":
Also, make sure you follow all the other steps mentioned in the video, and check out the other tutorial videos in the plugin, to help you set up your campaign properly.