Already mentioned in an answer is that ABS has a relatively large percentage of shrinkage (about 1.5 %), this should be encountered for in your model. So, the top layers width being smaller than the model is perfectly explained by the shrinkage.
It is also this shrinkage that causes the excess width layers at the bottom in combination with the heated bed temperature. The bed is of relative high temperature, this is close to the glass temperature of the filament, this ensures that the plastic is soft and adheres well to the build plate. But, this high temperature also causes that the material doesn't shrink much (the cooler, the higher the shrinkgae), the further away from the bed the lower the temperature the higher the shrinkage. This causes each layer to be a little smaller than the previous layer. As the part progresses layers are build upon layers fixating the layers, so the material at the lower layers will not shrink back when the whole part is cooled down (it will probably cause for some compression stress in the lower region).
This defect is known as "elephant foot" as e.g. explained in this answer. Basically the bed temperature is too high (but the downside is that ABS needs a high temperature to prevent warping and loosening from the build plate), too less cooling (also not something you want when printing ABS as cooling causes warping and prevents layers to stick well to each other) or a too low distance between the nozzle and the build plate. You could try lowering heated bed temperature by 5 °C each print, print with a raft and increasing the nozzle to build plate distance (leveling with a thicker piece of paper or increase the nozzle by redefinition of the
This is a common issue for high shrinkage, high temperature materials. It is something to live with, try to balance out the problem or adjust the print object by changing the design to include a chamfer at the bottom of the print.