Loading Spinner for layouts, panes and widgets. How should it look and feel?

Hi Panel Community

I have contributed a PR on loading spinners for Panel. Please help out make this awesome.

I would like to know how it should look and feel including which .gif to use. The height and width etc. The api for using it.

Feel free to write your suggestions here or in https://github.com/holoviz/panel/pull/1730