Top-Arrow: In style.css

.scroll_top i{
     background-color: #000000;
    border-radius: 100%;
    color: #FFFFFF;
    font-size: 16px;
    height: 30px;
    width: 30px;
    padding-top: 8px; //Changed this
    padding-right: 16px; //Changed this
    padding-bottom: 16px; //Changed this
    padding-left: 8px; //Changed this
    text-align: center;
}

Right/Left arrow: In Isotope.css

.meta-nav-next i, .meta-nav-prev i {
    border-radius: 3px;
    background: none repeat scroll 0 0 rgba(204, 204, 204, 0.4);
    padding: 1px; //Changed this to 1px
    height: 30px;
    width: 30px;
    line-height: 30px;
    font-size: 28px;
    text-align: center;
    margin-top: 3px;
}