What does class border-topbottom represent in the mobile solution for dealing with 1px?

what does class border-topbottom stand for in the solution where the mobile side deals with 1px?
this is the solution I found on the Internet, border.css,. He told me to add a class class where I want to add 1 pixel, but what direction should this border-topbottom class represent?

@ charset "utf-8";
.border,
.border-top,
.border-right,
.border-bottom,
.border-left,
.border-topbottom,
.border-rightleft,
.border-topleft,
.border-rightbottom,
.border-topright,
.border-bottomleft {

position: relative;

}
.border:: before,
.border-top::before,
.border-right::before,
.border-bottom::before,
.border-left::before,
.border-topbottom::before,
.border-topbottom::after,
.border-rightleft::before,
.border-rightleft::after,
.border-topleft::before,
.border-topleft::after,
.border-rightbottom::before,
.border-rightbottom::after,
.border-topright::before,
.border-topright::after,
.border-bottomleft::before,
.border-bottomleft::after {

content: "\0020";
overflow: hidden;
position: absolute;

}
/ * border

because the border is obscured by pseudo-element areas in the parent
therefore, if the child has interaction, it needs to set
Positioning and z-axis

* /
.border:: before {

box-sizing: border-box;
top: 0;
left: 0;
height: 100%;
width: 100%;
border: 1px solid -sharpeaeaea;
transform-origin: 0 0;

}
.border-top::before,
.border-bottom::before,
.border-topbottom::before,
.border-topbottom::after,
.border-topleft::before,
.border-rightbottom::after,
.border-topright::before,
.border-bottomleft::before {

left: 0;
width: 100%;
height: 1px;

}
.border-right::before,
.border-left::before,
.border-rightleft::before,
.border-rightleft::after,
.border-topleft::after,
.border-rightbottom::before,
.border-topright::after,
.border-bottomleft::after {

top: 0;
width: 1px;
height: 100%;

}
. Border-top::before,
.border-topbottom::before,
.border-topleft::before,
.border-topright::before {

border-top: 1px solid -sharpeaeaea;
transform-origin: 0 0;

}
. Border-right::before,
.border-rightbottom::before,
.border-rightleft::before,
.border-topright::after {

border-right: 1px solid -sharpeaeaea;
transform-origin: 100% 0;

}
. Border-bottom::before,
.border-topbottom::after,
.border-rightbottom::after,
.border-bottomleft::before {

border-bottom: 1px solid -sharpeaeaea;
transform-origin: 0 100%;

}
. Border-left::before,
.border-topleft::after,
.border-rightleft::after,
.border-bottomleft::after {

border-left: 1px solid -sharpeaeaea;
transform-origin: 0 0;

}
. Border-top::before,
.border-topbottom::before,
.border-topleft::before,
.border-topright::before {

top: 0;

}
. Border-right::before,
.border-rightleft::after,
.border-rightbottom::before,
.border-topright::after {

right: 0;

}
. Border-bottom::before,
.border-topbottom::after,
.border-rightbottom::after,
.border-bottomleft::after {

bottom: 0;

}
. Border-left::before,
.border-rightleft::before,
.border-topleft::after,
.border-bottomleft::before {

left: 0;

}
@ media (max--moz-device-pixel-ratio: 1.49), (- webkit-max-device-pixel-ratio: 1.49), (max-device-pixel-ratio: 1.49), (max-resolution: 143dpi), (max-resolution: 1.49dppx) {

/*  */

}
@ media (min--moz-device-pixel-ratio: 1.5) and (max--moz-device-pixel-ratio: 2.49), (- webkit-min-device-pixel-ratio: 1.5) and (- webkit-max-device-pixel-ratio: 2.49), (min-device-pixel-ratio: 1.5) and (max-device-pixel-ratio: 2.49), (min-resolution: 144dpi) and (max-resolution: 239dpi) (min-resolution: 1.5dppx) and (max-resolution: 2.49dppx) {

.border::before {
    width: 200%;
    height: 200%;
    transform: scale(.5);
}
.border-top::before,
.border-bottom::before,
.border-topbottom::before,
.border-topbottom::after,
.border-topleft::before,
.border-rightbottom::after,
.border-topright::before,
.border-bottomleft::before {
    transform: scaleY(.5);
}
.border-right::before,
.border-left::before,
.border-rightleft::before,
.border-rightleft::after,
.border-topleft::after,
.border-rightbottom::before,
.border-topright::after,
.border-bottomleft::after {
    transform: scaleX(.5);
}

}
@ media (min--moz-device-pixel-ratio: 2.5), (- webkit-min-device-pixel-ratio: 2.5), (min-device-pixel-ratio: 2.5), (min-resolution: 240dpi), (min-resolution: 2.5dppx) {

.border::before {
    width: 300%;
    height: 300%;
    transform: scale(.33333);
}
.border-top::before,
.border-bottom::before,
.border-topbottom::before,
.border-topbottom::after,
.border-topleft::before,
.border-rightbottom::after,
.border-topright::before,
.border-bottomleft::before {
    transform: scaleY(.33333);
}
.border-right::before,
.border-left::before,
.border-rightleft::before,
.border-rightleft::after,
.border-topleft::after,
.border-rightbottom::before,
.border-topright::after,
.border-bottomleft::after {
    transform: scaleX(.33333);
}

}

Css

May.22,2021