Create a visually striking flat design illustration of a cityscape enveloped in fog. The image should feature simplified geometric shapes representing buildings, with varying heights and colors to create depth and interest. The fog should be represented using soft gradients and muted tones, subtly obscuring the lower parts of the buildings while allowing the tops to peek through. Incorporate elements like trees and streetlights, rendered in a minimalist style, to enhance the urban environment. The overall composition should evoke a sense of calm and tranquility, with the fog creating a dreamlike atmosphere that invites viewers to explore the city. Keywords: "flat design," "cityscape fog," "minimalist illustration," "dreamlike atmosphere."