scroller {
    opacity   : .5;
    position  : absolute;
    height    : 72px;
    width     : 72px;
    background: url("/portale/Acommon/img/icons/arrowdown.png") center/72px 72px no-repeat;
    cursor    : pointer;
    -webkit-transition: opacity .9s, top 1s, bottom 1s;
       -moz-transition: opacity .9s, top 1s, bottom 1s;
        -ms-transition: opacity .9s, top 1s, bottom 1s;
         -o-transition: opacity .9s, top 1s, bottom 1s;
            transition: opacity .9s, top 1s, bottom 1s;
}

scroller:hover {
    opacity: 1;
}