The atmosphere of Venus is known to be very thick. In fact, it is three times thicker than the surface on earth. The reason why it is so thick is not only because of the carbon dioxide that can be found in the system. It is also because of the sulfuric acid clouds that line up the surface of the planet.
Take note that if you would try to look at the atmosphere of Venus, it will be hard to see its surface because the atmosphere is just very thick. The thickness of Venus's atmosphere makes it hard for the energy coming from the sun to penetrate the planet.