html,
body {
  height: 100%;
}

body {
  align-items: center;
  padding-top: 40px;
  padding-bottom: 40px;
  background-color: #f5f5f5;
}

/* // Medium devices (tablets, 768px and below) */
@media (max-width: 768px) {
  .btn{
    width: 100%;
  }
 }