twbs--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();
}