.demo{ background: #212121; } 

.btn{
    color: #adff2f;
    background: #1e1e1e;
    font-family: "Lobster", sans-serif;
    font-size: 22px;
    font-weight: 700;
    text-transform: capitalize;
    letter-spacing: 1.5px;
    margin: 0 10px;
    padding: 8px 15px;
    border: 0;
    border-radius: 10px;
    box-shadow: 0 0 10px #363636, inset 0 0 10px #363636;
    position: relative;
    z-index: 1;
    transition: 0.5s;
}

.btn:hover{ 
    color: #adff2f;
    animation: animate 0.5s 1 linear;
}

@keyframes animate {
     0% { transform: scale(0.7, 1.3); }
    25% { transform: scale(1.3, 0.7); }
    50% { transform: scale(0.7, 1.3); }
    75% { transform: scale(1.3, 0.7); }
   100% { transform: scale(1, 1);   }
}
  
@media only screen and (max-width: 767px){
    .btn{ margin-bottom: 30px; }
}