@media (min-width:768px){
 
.bounce {
 left: 50% ;
 padding-top: 60px;
 padding-bottom: 100px;
 animation: bounce 2s infinite;
 -webkit-animation: bounce 2s infinite;
 -moz-animation: bounce 2s infinite;
 -o-animation: bounce 2s infinite;
}
}

@media (max-width:320px){
.bounce {
 left: 50% ;
 padding-top: 20px;
 padding-bottom: 50px;
 animation: bounce 2s infinite;
 -webkit-animation: bounce 2s infinite;
 -moz-animation: bounce 2s infinite;
 -o-animation: bounce 2s infinite;
}
}
 
@-webkit-keyframes bounce {
 0%, 20%, 50%, 80%, 100% {-webkit-transform: translateY(0);} 
 40% {-webkit-transform: translateY(-30px);}
 60% {-webkit-transform: translateY(-15px);}
}
 
@-moz-keyframes bounce {
 0%, 20%, 50%, 80%, 100% {-moz-transform: translateY(0);}
 40% {-moz-transform: translateY(-30px);}
 60% {-moz-transform: translateY(-15px);}
}
 
@-o-keyframes bounce {
 0%, 20%, 50%, 80%, 100% {-o-transform: translateY(0);}
 40% {-o-transform: translateY(-30px);}
 60% {-o-transform: translateY(-15px);}
}
@keyframes bounce {
 0%, 20%, 50%, 80%, 100% {transform: translateY(0);}
 40% {transform: translateY(-30px);}
 60% {transform: translateY(-15px);}
}