v1/web/modules/contrib/bootstrap_layout_builder/scss/_mixins.scss

// Mixins
@mixin sr-only() {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0,0,0,0);
  border: 0;
}

@mixin smooth-all-transition() {
  transition: all .3s ease-in-out;
}

// Rounded input style
@mixin blb_box_inputs($width: 100%) {
  position: relative;
  flex: $width;
  width: $width;
  margin: 0;
  padding: 0;

  input {
    @include sr-only;

    + label {
      @include smooth-all-transition;
      border: 2px solid $panel_text_color;
      padding: 10px;
      height: 50px;
      width: 100%;
      display: flex;
      align-items: center;
      justify-content: center;
      text-align: center;
      cursor: pointer;

      &:hover {
        background-color: rgba($panel_text_color, .1);
      }
    }

    // Active state.
    &:checked + label {
      color: $panel_bg_color;
      background-color: $panel_text_color;
    }
  }

  // Custom fix for Bootstrap 3 Drupal theme.
  label {
    border: 2px solid $panel_text_color;
    height: 50px;
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    cursor: pointer;

    + input {
      opacity: 0;
      position: absolute;
    }

    // Active state.
    &.active {
      color: $panel_bg_color;
      background-color: $panel_text_color;
    }
  }
}