Use sphinx-design dropdowns to collapse long codelist tables

[duncandewhurst]

Some codelists are very long, e.g. mediaType, country, currency, which makes the codelist reference page hard to read.

[duncandewhurst]

One option is https://sphinx-toolbox.readthedocs.io/en/stable/extensions/collapse.html. However, it causes the codelist reference tables to overflow the width of the page.

[duncandewhurst]

https://github.com/executablebooks/sphinx-design provides a dropdown directive for hiding content in expandable containers.