Two things I notice very early on. The first is minor, but the app doesn't fill my screen horizontally on my ~5.75" screen, but it already feels stretched horizontally so I expect that this is a compromise and it's one that I'm fine with if no better solution can be found to both fill the screen and resolve the dimensions.
The second thing is a preference, it would be much better if the buttons in the top bar were larger. Pressing those buttons has always been the hardest part of using browser on mobile, and while it's much easier than in actual Chrome on mobile, it's still more difficult than I'd like. Those, especially the swap cities button and the farming villages button, are some of the most frequently-pressed buttons, so it would be nice if they were a bit easier to press, especially since there's so much dead space in that bar. Dead space is your enemy in designing mobile UI, especially in a game like this. There's always functionality for dead space.