1. The color and style of text works well against background.
2. The placement of text gets a bit tight for the mobile version especially for the 2nd and 3rd postcards.
3.Image for the last postcard is pixelated, so you might want to find a new image.
4. The line breaks for the 1st and last postcards are really nice but the 2nd feels a bit awkward in borth versions.
5. Like you did for the first postcard, maybe the width of the text could get narrower for the mobile versions for the other two as well.
6. Try experimenting with different placements of text as the viewing size gets smaller?
7. Image for the mobile version of the second postcard feels a bit tight with the text- maybe add some room to the top.