Bootstrap/scss/utilities/_display.scss

//
// Utilities for common `display` values
//

@each $breakpoint in map-keys($grid-breakpoints) {
  @include media-breakpoint-up($breakpoint) {
    $infix: breakpoint-infix($breakpoint, $grid-breakpoints);

    .d#{$infix}-none         { display: none !important; }
    .d#{$infix}-inline       { display: inline !important; }
    .d#{$infix}-inline-block { display: inline-block !important; }
    .d#{$infix}-block        { display: block !important; }
    .d#{$infix}-table        { display: table !important; }
    .d#{$infix}-table-cell   { display: table-cell !important; }
    .d#{$infix}-flex         { display: flex !important; }
    .d#{$infix}-inline-flex  { display: inline-flex !important; }
  }
}


//
// Utilities for toggling `display` in print
//

.d-print-block {
  display: none !important;

  @media print {
    display: block !important;
  }
}

.d-print-inline {
  display: none !important;

  @media print {
    display: inline !important;
  }
}

.d-print-inline-block {
  display: none !important;

  @media print {
    display: inline-block !important;
  }
}

.d-print-none {
  @media print {
    display: none !important;
  }
}