referentiel/src/demo.css

Convert position relative to a html element.

.pointer {
  width: 6px;
  height: 6px;
  background: red;
  position: absolute;
  border-radius: 50%;
}

.referentiel {
  width: 100px;
  height: 100px;
  background: pink;
  overflow: hidden;
  position: relative;
}

.marker {
  width: 10px;
  height: 10px;
  background: rgba(255, 0, 0, 0.5);
  position: fixed;
  border-radius: 50%;
}

.assert {
  position: absolute;
  width: 6px;
  height: 6px;
  background: black;
  position: absolute;
  border-radius: 50%;
}