according to this post: How to use Cesium Sandbox features?
I can use the sandcastle features in my app if I add https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/templates/bucket.css
https://sandcastle.cesium.com/Sandcastle-header.js
to my app. I will attempt to see if this is true as it may provide a way to do what I am trying to.
Update Edit: So adding the sandcastle-header.js to my app does allow me to make the dropdown menu like in sandcastle. I was previously under the impression that this wasn’t doable because of this post: Looking for documentation on Sandcastle Toolbar options - #2 by Hyper_Sonic