How to set up a border?

Question

css

There are 6 responsive blocks made on bootstrap, arranged in 2 rows of 3 respectively. It is necessary to make border-bottom for all blocks, except for the bottom row. It should be noted that when the screen is reduced, the blocks line up 2 in 3 rows and 1 in 6 rows. And all but the last row should have border-bottom.
nth-child(n+4) doesn't work.
The screenshot shows the code in SCSS.

Answer 1

&:nth-last-child (1,2,3) {border-bottom: white;}

media (min-width: @screen-sd) {
&:nth-last-child (3) {border-bottom: transparent;}
}
media (min-width: @screen-xs) {
&:nth-last-child (2) {border-bottom: transparent;}
  }

Answer 2

Alexander, I ask you to clarify one more point.
After installing your code, the following error message appeared: