Vulcan/packages/telescope-debug/lib/client/stylesheets/highlight.scss

.template-highlighter{
  position: absolute;
  border: 1px solid rgba(255,0,0,0.3);
  display: none;
  .show-highlighters &{
    display: block;
  }
  &:hover{
    // background: rgba(255,0,0,0.15);
    box-shadow: 0 0 0 99999px rgba(0, 0, 0, .2);
  }
}

.template-highlighter:hover:after{
  display: inline-block;
  content: attr(data-template);
  background:red;
  color:white;
  font-size:12px;
  position: absolute;
  bottom: 0px;
  right: 0px;
  z-index: 20000;
  padding: 2px 8px;
}

.zone-highlighter{
  border-color: rgba(0,0,255,0.3);
  &:hover{
    // background: rgba(0,0,255,0.15);
  }
}
.zone-highlighter:hover:after{
  background: blue;
}