debug.css

turbo-frame {
  border: 1px red solid;
  display: block;
}

turbo-frame::before {
  content: "Frame: #" attr(id);
  position: relative;
  top: -14px;
  right: -4px;
  display: inline-block;
  color: red;
  font-size: 12px;
  z-index: 9999;
  background-color: white;
  padding: 4px;
  border: 1px red solid;
}