ArcGIS Online was updated last night (June 27th) and as usual it includes enhancements and bug fixes for Story Maps!
Most of the enhancements are in Story Map Cascade, our increasingly popular full page scrolling narrative app. There's a new dark theme, font choices, support for tall images that your readers can scroll through, and the ability to optimize your Cascade for mobile viewing by specifying alternate media for story content that is unsupported or that doesn't work well on mobile. You can now also link directly to audio files to add sound to your Cascades. We've also added the most requested new feature for Story Map Shortlist (beta): the ability to choose the color of the header to tailor the look of your Shortlist. A number of issues in the Shortlist beta were also addressed, and you can now create Shortlists correctly from places defined in an ArcGIS Enterprise Server point feature service.
Read the blog post...
and here's where to read about all the other new features this ArcGIS Online update introduces: