Why does not beamer cover math contents in `align` when setting covered content to `transparent`?
How to change the opacity of a surface out of a rectangular area?
How to make some character "unreadable" as text in the pdf output but still visible?
How to make a block transparent but not its title?
How to make document background non-transparent?
How to make a background picture transparent?
How can I create a transparent background in a logo?