Bootstrap/scss/_grid.scss

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

@if $enable-grid-classes {
  .container {
    @include make-container();
    @include make-container-max-widths();
  }
}

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

@if $enable-grid-classes {
  .container-fluid {
    @include make-container();
  }
}

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

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


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

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


// Flex variation
//
// Custom styles for additional flex alignment options.

@if $enable-flex and $enable-grid-classes {

  // Flex column reordering

  @each $breakpoint in map-keys($grid-breakpoints) {
    @include media-breakpoint-up($breakpoint) {
      .col-#{$breakpoint}-first { order: -1; }
      .col-#{$breakpoint}-last  { order: 1; }
    }
  }

  // Alignment for every column in row

  @each $breakpoint in map-keys($grid-breakpoints) {
    @include media-breakpoint-up($breakpoint) {
      .row-#{$breakpoint}-top    { align-items: flex-start; }
      .row-#{$breakpoint}-center { align-items: center; }
      .row-#{$breakpoint}-bottom { align-items: flex-end; }
    }
  }

  // Alignment per column

  @each $breakpoint in map-keys($grid-breakpoints) {
    @include media-breakpoint-up($breakpoint) {
      .col-#{$breakpoint}-top    { align-self: flex-start; }
      .col-#{$breakpoint}-center { align-self: center; }
      .col-#{$breakpoint}-bottom { align-self: flex-end; }
    }
  }
}