Hi Michael, if you set a max-width of 300px on the BasemapGallery's container then it should stay in the list view.
Here's an example: https://codepen.io/annefitz/pen/rNbRZPP?editors=1000
The BasemapLayerList widget is different - it does not allow you to switch basemap styles but instead displays the layers within your current basemap and allows you to toggle their visibility, similar to the LayerList widget.
Hope this helps!