Tara, we just released an update to the playlist app a couple days ago so make sure you have the most recent version before continuing. Before adding additional widgets to the app we recommend thinking about what value they will give to the end user. Adding too many options can sometime confuse the user more than help them. That being said, there are reasons to add additional basemap options. However, we recommend limiting the number of basemaps to the two or three most useful ones.
The easiest way to add a basemap gallery is to use the Basemap dijit included in the ArcGIS API for JavaScript (Documentation here). The basemap gallery requires access to the map object as well as a div within the html where the basemap galley will go.
In the playlist, the map components live in the Map.js file (source > app > javascript > playlist > ui > Map.js). You can place the basemap gallery code after the arcgis.createmap function and response function. Then use "_map" as the map object when configuring the basemap gallery.
To create a space in the side panel for the basemap gallery, you can follow these instructions: Re: Additional side pane toggle/widow in Playlist Story Map
One of the basemap gallery options is "basemaps." Use this to limit the basemaps in your gallery.
