.zh-backtotop {
    position: fixed;
    bottom: 80px;
    left: 52%;
    z-index: 19;
    margin-left: 460px;
}

.zh-backtotop .btn-action {
    display: block;
    width: 56px;
    height: 56px;
    background-color: #ff5722;
    border-radius: 28px;
    border: 0;
    cursor: pointer;
    position: relative;
    box-shadow: 0 0 4px rgba(0, 0, 0, .14), 0 4px 8px rgba(0, 0, 0, .2);
    -moz-box-shadow: 0 0 4px rgba(0, 0, 0, .14), 0 4px 8px rgba(0, 0, 0, .2);
    -webkit-box-shadow: 0 0 4px rgba(0, 0, 0, .14), 0 4px 8px rgba(0, 0, 0, .2);
}

.zh-backtotop .btn-action+.btn-action {
    margin-top: 5px
}

.zh-backtotop div {
    position: absolute;
    right: 0;
    left: 0;
    margin: auto
}

.zh-backtotop .arrow {
    position: absolute;
    top: 16px;
    left: 16px;
}

.zh-backtotop .btn-action:hover {
    background-color: #e24134;
    box-shadow: 0 0 6px rgba(0, 0, 0, .16), 0 4px 10px rgba(0, 0, 0, .22);
    -moz-box-shadow: 0 0 6px rgba(0, 0, 0, .16), 0 4px 10px rgba(0, 0, 0, .22);
    -webkit-box-shadow: 0 0 6px rgba(0, 0, 0, .16), 0 4px 10px rgba(0, 0, 0, .22);
}

@media (max-width: 1024px) {
    .zh-backtotop {
        margin: auto;
        left: auto;
        right: 1em;
        bottom: 1em
    }
}

@media (max-width:979px) {
    .zh-backtotop {
        margin: auto;
        left: auto;
        right: 1em;
        bottom: 1em
    }
}

@media (max-width:768px) {
    .zh-backtotop {
        margin: auto;
        left: auto;
        right: 1em;
        bottom: 1em
    }
}

@media (max-width: 550px) {
    .zh-backtotop .btn-action {
        width: 48px;
        height: 48px;
    }

    .zh-backtotop .arrow {
        top: 12px;
        left: 12px;
    }
}

@media (max-width: 320px) {
    .zh-backtotop .btn-action {
        width: 40px;
        height: 40px;
    }

    .zh-backtotop .arrow {
        top: 8px;
        left: 8px;
    }
}