html, body {
  
  padding: 20px;
  
}
body{
  margin:auto;
  width: 90%;
  align:center;
}
#golpe{
  font-size: 30px;
  text-align: center;
  
}
#btn {
  background-color:#008CBA; /* azul */
  border: none;
  color: white;
  padding: 15px 32px;
  text-align: center;
  text-decoration: none;
  display:block;
  margin:auto;
  font-size: 16px;
  border-radius: 25px;
  box-shadow: 0 8px 16px 0 rgba(0,0,0,0.2), 0 6px 20px 0 rgba(0,0,0,0.19);
}
footer {
    position: fixed;
    left: 0;
    bottom: 0;
    width: 100%;
    padding: 10px;
}