Of the type-of-1.first : First eg: selected in the first div p, p, and the first outside the div.
2.last-of-type (the last one)
Foreigners counts from 0
3.nth-of-type (number) number downwardly from eg: nth-of-type (1) select the second
4.ntn-last-of-type (number) number from the bottom egnth-last-of-type (1): penultimate
5.first-child: a first sub-element, and it must be the first position, the position subject to the influence of other elements eg: p: first-child 
There may be a plurality of values, both when under a different parent, and in the first p
6.last-child
7.nth-child(number):
Using the above selector do: 
you can select any of a commodity while two lines, used here as a clear margin
♥ nth-child (n) nth-of-type nth-last-of-type brackets which can put n (Select), 2n + 1 (odd) 2N (even-numbered) with 3N (multiple of 3)