twbs--bootstrap/scss/_grid.scss

// Row
//
// Rows contain your columns.

@if $enable-grid-classes {
  .row {
    @include make-row();

    > * {
      @include make-col-ready();
    }
  }
}

@mixin make-cssgrid($columns: $grid-columns, $breakpoints: $grid-breakpoints) {
  @each $breakpoint in map-keys($breakpoints) {
    $infix: breakpoint-infix($breakpoint, $breakpoints);

    @include media-breakpoint-up($breakpoint, $breakpoints) {
      @if $columns > 0 {
        @for $i from 1 through $columns {
          .g-col#{$infix}-#{$i} {
            grid-column: auto / span $i;
          }
        }

        // `$columns - 1` because offsetting by the width of an entire row isn't possible
        @for $i from 0 through ($columns - 1) {
          .g-start#{$infix}-#{$i} {
            grid-column-start: $i;
          }
        }
      }
    }
  }
}

@if $enable-cssgrid {
  .grid {
    display: grid;
    grid-template-rows: repeat(var(--#{$variable-prefix}rows, 1), 1fr);
    grid-template-columns: repeat(var(--#{$variable-prefix}columns, #{$grid-columns}), 1fr);
    gap: var(--#{$variable-prefix}gap, #{$grid-gutter-width});

    @include make-cssgrid();
  }
}


// Columns
//
// Common styles for small and large grid columns

@if $enable-grid-classes {
  @include make-grid-columns();
}