Grid

Gap

column-gap

CSS
.container {
  display: grid;
  grid-template: repeat(3, 1fr) / repeat(4, 1fr);
  column-gap: 20px;
}
Box-1
Box-2
Box-3
Box-4
Box-5
Box-6
Box-7
Box-8
Box-9

row-gap

CSS
.container {
  display: grid;
  grid-template: repeat(3, 1fr) / repeat(4, 1fr);
  row-gap: 20px;
}
Box-1
Box-2
Box-3
Box-4
Box-5
Box-6
Box-7
Box-8
Box-9

gap

CSS
.container {
  display: grid;
  grid-template: repeat(3, 1fr) / repeat(4, 1fr);
  gap: 40px 20px;   // row column
Box-1
Box-2
Box-3
Box-4
Box-5
Box-6
Box-7
Box-8
Box-9
CSS
.container {
  display: grid;
  grid-template: repeat(3, 1fr) / repeat(4, 1fr);
  gap: 20px;   // both row and column
Box-1
Box-2
Box-3
Box-4
Box-5
Box-6
Box-7
Box-8
Box-9