Bootstrap/scss/_debug.scss

@if $enable-debugger-classes {
  %grid-debug {
    position: relative;

    &::before {
      position: absolute;
      top: 0;
      right: 0;
      bottom: 0;
      left: 0;
      z-index: 1999;
      pointer-events: none;
      content: "";
      background: repeating-linear-gradient(to right, transparent, transparent calc(var(--#{$prefix}gutter-x) * .5), var(--#{$prefix}primary) calc(var(--#{$prefix}gutter-x) * .5), var(--#{$prefix}primary) calc((100% - 12 * var(--#{$prefix}gutter-x)) / 12 + var(--#{$prefix}gutter-x) * .5), transparent calc((100% - 12 * var(--#{$prefix}gutter-x)) / 12 + var(--#{$prefix}gutter-x) * .5), transparent calc(100% / 12)); // stylelint-disable-line function-disallowed-list
      opacity: .3;
    }
  }

  .#{$prefix}debug-grids {
    &::before {
      position: fixed;
      top: 0;
      left: 0;
      z-index: 2000;
      padding: .5em 1em;
      font-family: $font-family-base;
      color: $black;
      background-color: $white;
      border-radius: 0 0 4px; // stylelint-disable-line property-disallowed-list
      @include font-size(var(--#{$prefix}debug-label-font-size, $h1-font-size));
    }

    @each $breakpoint, $value in $grid-breakpoints {
      @include media-breakpoint-up($breakpoint) {
        &::before {
          content: "#{$breakpoint}";
        }
      }
    }

    [class^="container"],
    &[class^="container"],
    .row,
    &.row {
      @extend %grid-debug;
    }
  }

  .#{$prefix}debug-grid-cols {
    @extend %grid-debug;
  }
}