message: implemented same treatment for add and root add buttons in diagram.
  Fixes
diff: @import '../_styles';
  +@import (reference) '../../../../assets/_variables';
  :host {
  .tile-container();
  .btn-insert {
  .tile-placeholder;
  .flex-center;
  - color: #b6d9ed;
  + color: @color-secondary;
  + background-color: transparent;
  + border: 2px dashed @color-secondary;
  + box-shadow: none;
  + &:hover {
  + color: @columbia-blue;
  background-color: @tile-color-bg;
  + transform: translateY(-2px);
  + outline: none;
  box-shadow: 0 1px 3px 0 rgba(0, 0, 0, 0.3);
  transition: all 0.25s ease;
  - outline: none;
  -
  - &:hover {
  - box-shadow: 0 5px 16px 1px rgba(0, 0, 0, 0.2);
  - transform: translateY(-2px);
  + border: none;
  }
  &:focus {
  width: @tile-placeholder-dimension / 3;
  }
  -:host(.is-root) {
  - .btn-insert {
  - color: #79b8dc;
  - background-color: transparent;
  - border: 2px dashed #79b8dc;
  - box-shadow: none;
  - }
  - .btn-insert:hover {
  - background-color: @tile-color-bg;
  - }
  -}
  :host(.is-selected) {
  .btn-insert, .btn-insert:hover {
  - box-shadow: 1px 2px 9px 0px rgba(0, 0, 0, 0.3);
  + box-shadow: 1px 2px 9px 0 rgba(0, 0, 0, 0.3);
  transform: translateY(0);
  background-color: @tile-color-bg--selected;
  - color: #fff;
  + color: @color-bg;
  border: none;
  }
  }
  