If you've a suitable image you can and want to use (importing an entire spiral galaxy will likely crash your computer ?), and it's available to you as a standard image file (jpg, png, bmp), you can simply create a new Sheet in your CC3+ drawing, and then import it into that using the Draw - Insert File command from the drop-down menus. Give the Sheet a recognisable name so you can find it easily when you need to turn it on and off. You may need to resize the image to get it to fit the size of your drawing properly, but that's fairly easily done, if a bit fiddly to get exactly right.

You would probably be best to also set the file image up on a separate Layer too, but that's not essential.

If you do go down the "shadowed line" route, you'll probably need to fiddle about with a mask for part of the pit too, to stop the shadow going into places outside it you don't want - sadly, I remembered that only about ten minutes after I came offline yesterday...

Also - just seen this now - there's a gap at the SE corner of room 16. That may have happened when you cut the wall to insert the open doorway if you started the wall at the corner of the room originally. I learnt from one of Joe Sweeney's videos early on to always start a dungeon wall along one of the straights you won't be cutting a doorway into later, to avoid exactly this kind of issue. It's also easily forgotten when you're busy drawing walls, however, as I've discovered ?.

Don't know whether the newly-released "coffin box" version of Strahd adds or changes anything to this. From what previews I've seen, they've reverted to a nice foldout poster map, but the layout looked pretty similar to most previous versions overall. Couldn't see enough to check in detail, of course. For that, there's the little matter of $99.99 to pay first...

There are some coloured swirls in the CA3 Magic symbols. I thought there might be some among the Elemental & Magic Symbols in DD3, but I've had no luck trying to quickly track any down.

Interesting, but in comparison with your existing forests, it looks a little like a marsh on top of a low plateau. If that was the only style of forest symbol though, it would probably be fine.

Being honest, I prefer your individual, variable-tree-size forests on this map, however.