POLAR@3: Default style for polar-map element

[oeninghe-dataport]

Current situation:

There is no default style for the polar-map element.

Proposal:

We define a default style for the polar-map element.
The style should not be too opinionated, however, using polar-map and have it visible should work OOTB.

[oeninghe-dataport]

It is necessary to allow overriding the style easily from external (not-shadowed) CSS.

The default style should consist of display, width and height.

Weekly

[oeninghe-dataport]

This will be tracked further at #378