* {
  position: relative;
}

body {
  font-family: sans-serif;
}
#demo {
  border: 1px solid black;
  width: 600px;
  height: 600px;
}

p {
  font-size: 1.4em;
}
.line {
  position: absolute;
  width: 1px;
  height: 600px;
  left: 300px;
  background: black;
}

.box {
  position: absolute;
  width: 50px;
  height: 50px;
  background: dodgerblue;
  border-radius: 10px;
  left: 275px;
  top: 275px;
}

.box path {
  fill: white;
}

.box svg {
  transform: scale(0.8);
}

.box,
.line {
  pointer-events: none;
}