.topnav {
  overflow: hidden;
  background-color: #f1f1f1;
}

.topnav a {
  float: left;
  display: block;
  color: black;
  text-align: center;
  padding: 10px 12px;
  text-decoration: none;
  font-size: 15px;
  border-bottom: 3px solid transparent;
}

.topnav a:hover {
  border-bottom: 3px solid red;
}

.topnav a.active {
  border-bottom: 3px solid red;
}

pre {
    white-space: pre-wrap;
}


.show_on_hover {
  /* display: none; */
  block-size: 15px;
  overflow: hidden;
}

.hover_to_show:hover + .show_on_hover {
  /* display: block; */
  block-size: auto;
}


.hover_to_expand {
  block-size: 40px;
  overflow: hidden;
}

.hover_to_expand:hover {
  block-size: auto;
}