sass/components/_button-group.scss
.#{$prefix}btn-group, .#{$prefix}btn-group-vertical {
  display: inline-block;
  vertical-align: middle;
  > .dxy-btn:not(:first-child):not(:last-child) {
    border-radius: 0;
  }
  .dxy-btn:disabled {
    border-color: $btn-bd-color;
  }
}

.#{$prefix}btn-group {
  > .dxy-btn {
    float: left;
  }
  .dxy-btn + .dxy-btn {
    margin-left: -1px;
  }
  > .dxy-btn:first-child:not(:last-child) {
    border-top-right-radius: 0;
    border-bottom-right-radius: 0;
  }
  > .dxy-btn:last-child:not(:first-child) {
    border-top-left-radius: 0;
    border-bottom-left-radius: 0;
  }
  .dxy-btn:not(:last-child) {
    margin-right: -1px;
  }
  /*.dxy-btn + .dxy-btn {
    margin-left: 0;
  }*/
  .dxy-btn-primary:first-child {
    border-right-color: rgba(0, 0, 0, 0.2);
  }
  .dxy-btn-primary:not(:first-child):not(:last-child) {
    border-left-color: rgba(0, 0, 0, 0.2);
    border-right-color: rgba(0, 0, 0, 0.2);
  }
  .dxy-btn-primary:last-child {
    border-left-color: rgba(0, 0, 0, 0.2);
  }

}

.#{$prefix}btn-group-vertical {
  > .dxy-btn {
    display: block;
    width: 100%;
    max-width: 100%;
  }
  .dxy-btn + .dxy-btn {
    margin-top: -1px;
  }
  > .dxy-btn:first-child:not(:last-child) {
    border-top-left-radius: $button-group-radius;
    border-top-right-radius: $button-group-radius;
    border-bottom-right-radius: 0;
    border-bottom-left-radius: 0;
  }
  > .dxy-btn:last-child:not(:first-child) {
    border-top-left-radius: 0;
    border-top-right-radius: 0;
    border-bottom-right-radius: $button-group-radius;
    border-bottom-left-radius: $button-group-radius;
  }
}