Generating custom:button-card code with JavaScript

Configuration Frontend
1

I am trying to generate custom:button-card elements "on the fly" with JavaScript. It works well with single variables:

variables:
  iconColor: "[[[ return '#d0d000'; ]]]"
...
styles:
  icon:
    color: "[[[ return variables.iconColor; ]]]"

And it works well with arrays:

variables:
  objectTemplates: |
    [[[
      return ['FLEXIBOX-OBJECT', 'OBJECT-TYPE-BUTTON'];
    ]]]
...
custom_fields:
  OBJECT:
    card:
      - type: custom:button-card
        template: "[[[ return variables.objectTemplates; ]]]"

But I haven't managed to work out if it's possible to return a dictionary/map (whatever the terminology is) from a variable - conceptually I'm trying to achieve this:

variables:
  myMap: |
    [[[
      return {
        'border-radius': '16px',
        'padding': '16px',
        'overflow': 'hidden'
      };
    ]]]
...
styles:
  card: "[[[ return variables.myMap; ]]]"    <-- this doesn't work!

I have tried to find documentation about this, but it seems this is a somewhat unusual use case for button-card variables... I'm not even sure maps are natively supported data structures in JavaScript. Anyone managed to achieve something like this?