Bootstrap/scss/layout/_containers.scss

@use "../config" as *;
@use "breakpoints" as *;

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

@mixin make-container($gutter: $container-padding-x) {
  --#{$prefix}gutter-x: #{$gutter};
  --#{$prefix}gutter-y: 0;
  width: 100%;
  padding-right: calc(var(--#{$prefix}gutter-x) * .5);
  padding-left: calc(var(--#{$prefix}gutter-x) * .5);
  margin-right: auto;
  margin-left: auto;
}

@layer layout {
  @if $enable-container-classes {
    // Single container class with breakpoint max-widths
    .container,
    // 100% wide container at all breakpoints
    .container-fluid {
      @include make-container();
    }

    // Responsive containers that are 100% wide until a breakpoint
    @each $breakpoint, $container-max-width in $container-max-widths {
      .container-#{$breakpoint} {
        @extend .container-fluid;
      }

      @include media-breakpoint-up($breakpoint, $breakpoints) {
        %responsive-container-#{$breakpoint} {
          max-width: $container-max-width;
        }

        // Extend each breakpoint which is smaller or equal to the current breakpoint
        $extend-breakpoint: true;

        @each $name, $width in $breakpoints {
          @if ($extend-breakpoint) {
            .container#{breakpoint-infix($name, $breakpoints)} {
              @extend %responsive-container-#{$breakpoint};
            }

            // Once the current breakpoint is reached, stop extending
            @if ($breakpoint == $name) {
              $extend-breakpoint: false;
            }
          }
        }
      }
    }
  }
}