.copyright
{
    bottom: 0;            /* <-- important */
    left: 0;
    right: 0;
    margin: 0;
    padding-bottom: 0;
    margin-bottom: 0;
}
.copyright p
{
    text-align: center;
    padding: 28px;
    color: black;
    background-color: grey;
    margin: 0;
    font-family: 'Inter', sans-serif;
}

@media (max-width: 640px){
  .copyright p{
    padding: 18px;
    font-size: 14px;
  }
}