for the past several days, most or all of the kingdom cards as well as the cards in my hand have been blacked out so that I cannot see them. What's going on?
Is the whole card blacked out, or "only" the picture? There have been reports of totally black cards when looking at the trash window, but not for cards is hand.
If it is "only" the picture, that points to some connection/bandwidth issue, where the browser gives up waiting for the card art to arrive (which is the most bandwidth intensive part of the game start).
In such a case, using a page reload (CTRL-R on Firefox/Chrome, Command-Alt-R on Safari) should help, assuming the underlying connection issue is no longer true.