custom styles for {{item}}/viewcontent

[phette23]

see example at: https://vault.cca.edu/items/d334834e-6bf6-40b3-b94e-68102aa6e7e1/1/viewcontent

/viewcontent is basically a simple attachment viewer for items but we could customize it to work a bit better. Apparently this is used in third-party integrations (e.g. with Blackboard) so we wouldn't want to deck it out too much, though. Annemarie probably has an idea of what she wants.