comment/lib/components/Editor/Emoji.css

.item {
  float: left;
  width: 40px;
  height: 40px;
  cursor: pointer;
  white-space: nowrap;
  /* this is required unless you put the helper span closely near the img */
  text-align: center;
  margin: 0;
}
.item .helper {
  display: inline-block;
  height: 100%;
  vertical-align: middle;
}
.item img {
  margin: 0 auto;
  vertical-align: middle;
  padding: 3px;
}
.item img:hover {
  border: 1px solid #40a9ff;
}