Fills are only available in the map they belong in by default. To use fills from other map types, they need to be imported into the map first. Quickest option here is to use Draw -> Insert file and insert a map file from the style containing the appropriate fills. Note that once you have the map on the cursor ready to place, you can just hit Esc instead of actually placing it, once you've gotten to that stage, the fill definitions have actually been copied.

As for Sue's snow, as she says in her post, it is using a solid color pale blue fill, so no special fills at all needed for that one.

Four new maps in the atlas from the contest. This time it is the excellent contribution from @Arcwynd.

Thanks. I still have quite a large backlog to work through, so I'll put it in the queue.

Lost Temple of Winter by @Lizzy_Maracuja is now in the atlas. Thanks for contributing and participating in the contest.

I am slowly but surely working through all the competition maps.

City styles aren't really made for showing interior details, so it doesn't work like that by default.

However,there isn't anything preventing you from drawing building interiors, and then but the building sheet on top of them. So, with the building sheet visible, it will cover up the floorplans and look like a normal city, and with the building sheet hidden, you will see the floor plans. All you need to do is to set up proper sheets to draw your floor plans on, and import the required fill styles into your map.

A word of warning here though, mapping the interior of every building in a large city is time consuming, and also results in a lot of entities that can cause CC3+ to slow down. You can avid the latter partially by making sure the interior sheet is hidden when it is not in use (as in actualy hidde, not just covered up by the buildings sheet). For a smaller place, this may work perfectly fine, but I don't recommend it for larger cities.

Instead, I would make some detailed sections of the city as maps like this.

Also note that CD3 can automatically take a building symbol and make a floorplan from it on it's own map. This map is then linked from the city map so you can just click on it to go to the floor plan map. This is the preferred way of making florplans for houses. Note that it only generates the outline of the floorplan, it won't greate a fully furnished plan for you.