25% { background-position: -2px 3px; } 50% { background-position: -2px 6px; } 75% { background-position: -2px 9px; } 100% { background-position: -2px 12px; } } .icon_download { position: relative; @extend %icon; width: 11px; height: 12px; @include bg_url($url: 'icons/btn/download.png'); &:after { display: none; position: absolute; top: 0; left: 2px; width: 7px; height: 9px; @include bg($color: #e6e6e6, $url: 'icons/btn/download_hover.png'); content: ''; } .btn:hover & { @include bg_url($url: 'icons/btn/download_hover.png'); &:after { display: block; animation: download 1s infinite; } } } demo http://static.paipaiimg.com/v5/html/pms/page.html