Bootstrap/scss/forms/_layout.scss

// Form grid
//
// Special replacement for our grid system's `.row` for tighter form layouts.

@if $enable-grid-classes {
  .form-row {
    display: flex;
    flex-wrap: wrap;
    margin-right: -$form-grid-gutter-width / 2;
    margin-left: -$form-grid-gutter-width / 2;

    > .col,
    > [class*="col-"] {
      padding-right: $form-grid-gutter-width / 2;
      padding-left: $form-grid-gutter-width / 2;
    }
  }
}

// Inline forms
//
// Make forms appear inline(-block) by adding the `.form-inline` class. Inline
// forms begin stacked on extra small (mobile) devices and then go inline when
// viewports reach <768px.
//
// Requires wrapping inputs and labels with `.form-group` for proper display of
// default HTML form controls and our custom form controls (e.g., input groups).

.form-inline {
  display: flex;
  flex-flow: row wrap;
  align-items: center; // Prevent shorter elements from growing to same height as others (e.g., small buttons growing to normal sized button height)

  // Because we use flex, the initial sizing of checkboxes is collapsed and
  // doesn't occupy the full-width (which is what we want for xs grid tier),
  // so we force that here.
  .form-check {
    width: 100%;
  }

  // Kick in the inline
  @include media-breakpoint-up(sm) {
    label {
      display: flex;
      align-items: center;
      justify-content: center;
      margin-bottom: 0;
    }

    // Inline-block all the things for "inline"
    .form-group {
      display: flex;
      flex: 0 0 auto;
      flex-flow: row wrap;
      align-items: center;
      margin-bottom: 0;
    }

    // Allow folks to *not* use `.form-group`
    .form-control {
      display: inline-block;
      width: auto; // Prevent labels from stacking above inputs in `.form-group`
      vertical-align: middle;
    }

    // Make static controls behave like regular ones
    .form-control-plaintext {
      display: inline-block;
    }

    .input-group,
    .form-select {
      width: auto;
    }

    // Remove default margin on radios/checkboxes that were used for stacking, and
    // then undo the floating of radios and checkboxes to match.
    .form-check {
      display: flex;
      align-items: center;
      justify-content: center;
      width: auto;
      padding-left: 0;
    }
    .form-check-input {
      position: relative;
      flex-shrink: 0;
      margin-top: 0;
      margin-right: $form-check-input-margin-x;
      margin-left: 0;
    }
  }
}