// bootstrap.css

.btn-gray {
  color: #fff;
  background-color: #6c7074;
  border-color: #6c7074;
}
.btn-gray:hover {
  color: #fff;
  background-color: #5a5d60;
  border-color: #53575a;
}
.btn-gray:focus, .btn-gray.focus {
  box-shadow: 0 0 0 0.2rem rgba(108, 112, 116, 0.5);
}
...