Bootstrap/scss/mixins/_grid.scss

/// Grid system
//
// Generate semantic grid columns with these mixins.

@mixin make-container($gutter: $grid-gutter-width) {
  margin-right: auto;
  margin-left: auto;
  padding-left:  ($gutter / 2);
  padding-right: ($gutter / 2);
  @include clearfix();
}

@mixin make-row($gutter: $grid-gutter-width) {
  margin-left:  ($gutter / -2);
  margin-right: ($gutter / -2);
  @include clearfix();
}

@mixin make-col($gutter: $grid-gutter-width) {
  position: relative;
  float: left;
  min-height: 1px;
  padding-left:  ($gutter / 2);
  padding-right: ($gutter / 2);
}

@mixin make-col-span($columns) {
  width: percentage(($columns / $grid-columns));
}

@mixin make-col-offset($columns) {
  margin-left: percentage(($columns / $grid-columns));
}

@mixin make-col-push($columns) {
  left: percentage(($columns / $grid-columns));
}

@mixin make-col-pull($columns) {
  right: percentage(($columns / $grid-columns));
}