.book1{animation:mymove 5s infinite}@keyframes mymove{0%{top:0px}50%{top:30px}100%{top:0px}}.book2{animation:mymove 4s infinite}@keyframes mymove{0%{top:0px}50%{top:10px}100%{top:0px}}.book3{animation:mymove 5s infinite}@keyframes mymove{0%{top:0px}50%{top:30px}100%{top:0px}}.book4{animation:mymove 4s infinite}@keyframes mymove{0%{top:0px}50%{top:30px}100%{top:0px}}