Getting the class of all columns of data.frames in a list

Question

Example Data:

df1 <- as.data.frame(rbind(c(1,2,3), c(1, NA, 4), c(NA, NA, NA), c(4,6,7), c(4, 8, NA)))
df2 <- as.data.frame(rbind(c(1,2,3), c(1, NA, 4),