.boton_bola {
  background-color: #000000;
  border: 2px solid #000000;
  border-radius: 200px 200px 200px 200px;
  -moz-border-radius: 200px 200px 200px 200px;
  -webkit-border-radius: 200px 200px 200px 200px;
  box-shadow: 5px 5px 5px 0px rgba(0,0,0,0.5);
  color: #000000;
  padding: 15px 15px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 24px;
}