Add styling to the missing class in the Adventure builder to make it more clear when a Document is missing in the world

[mattexdee]

User Experience

Currently .sheet.adventure-exporter .tab.contents h4.add, .sheet.adventure-exporter .tab.contents h4.update, and .sheet.adventure-exporter .tab.contents h4.remove are styled with green, white, and red to indicate their status. We also add .missing for documents which are no longer present in the world but there's no styling associated with them. By using a color like yellow we could make it more clear which Documents are at risk of being lost during an Adventure rebuild.

For example:

It might also be worth adding a data-tooltip value that explains each document's status on hover.