Bootstrap/scss/_grid.scss

//
// Grid system
// --------------------------------------------------


// Container widths
//
// Set the container width, and override it for fixed navbars in media queries.

.container {
  @include make-container();

  // For each breakpoint, define the maximum width of the container in a media query
  @each $breakpoint, $container-max-width in $container-max-widths {
    @include media-breakpoint-up($breakpoint) {
      max-width: $container-max-width;
    }
  }
}


// Fluid container
//
// Utilizes the mixin meant for fixed width containers, but without any defined
// width for fluid, full width layouts.

.container-fluid {
  @include make-container();
}


// Row
//
// Rows contain and clear the floats of your columns.

.row {
  @include make-row();
}


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

@include make-grid-columns();

// Flex column reordering
@if $enable-flex {
  .col-xs-first { order: -1; }
  .col-xs-last { order: 1; }

  @include media-breakpoint-up(sm) {
    .col-sm-first { order: -1; }
    .col-sm-last { order: 1; }
  }

  @include media-breakpoint-up(md) {
    .col-md-first { order: -1; }
    .col-md-last { order: 1; }
  }

  @include media-breakpoint-up(lg) {
    .col-lg-first { order: -1; }
    .col-lg-last { order: 1; }
  }

  @include media-breakpoint-up(xl) {
    .col-xl-first { order: -1; }
    .col-xl-last { order: 1; }
  }
}