Vanilla.js style

style.css

body {
  font-family: sans-serif, arial, helvetica;
}

button {
  cursor: pointer;
  margin-top: 1em;
  padding: 1em;
  border-radius: 50%;
}

div.post {
  border-top: solid black 2px;
}

h1 {
  width: 95%;
  font-size: 1.5em;
  background: lightgray;
  padding: 0.2em;
  text-align: justify;
}

p {
  margin-left: 2em;
}

.tooltip {
  position: relative;
  display: inline-block;
  border-bottom: 1px dotted black;
}

.tooltip .tooltiptext {
  visibility: hidden;
  background-color: gray;
  color: #fff;
  text-align: center;
  padding: 5px;
  margin-left: -5px;
  border-radius: 6px;
  position: absolute;
  z-index: 1;
}

.tooltiptext:hover {
  visibility: visible;
}

.tooltip:hover .tooltiptext {
  visibility: visible;
}