body {
  font-family: sans-serif;
}

#app {
  display: flex;
  flex-flow: column wrap;
  align-items: center;
}
#btn {
  width: 100px;
  height: 32px;
  border-radius: 20px;
  border: 2px solid black;
  position: relative;
  margin: 40px 0;
  cursor: pointer;
  box-shadow: 0 0 10px 2px black;
}
#span {
  width: 25px;
  height: 25px;
  border-radius: 50%;
  background-color: black;
  position: absolute;
  left: 15%;
  top: 50%;
  transform: translate(-50%, -50%);
}
h1 {
  font-size: 2.5rem;
  font-family: serif;
}
body {
  background-color: white;
  color: black;
}