.powered {
  position: absolute;
  bottom: 25px;
  left: 0;
  width: 100%;
  text-align: center;
}

.powered img {
  margin-left: 5px;
  vertical-align: middle;
}

.btn-cnx {
  width: 45%;
  display: block;
  margin: 1.5rem auto 0; /* 1.5rem = mt-4 équivalent */
}