#return-to-top-Nht {
    position: fixed;
    bottom: 20px;
    right: 20px;
    background: #e60000;
    /*background: rgba(0, 0, 0, 0.7);*/
    width: 50px;
    height: 50px;
    display: block;
    text-decoration: none;
    -webkit-border-radius: 35px;
    -moz-border-radius: 35px;
    border-radius: 35px;
    display: none;
    -webkit-transition: all 0.3s linear;
    -moz-transition: all 0.3s ease;
    -ms-transition: all 0.3s ease;
    -o-transition: all 0.3s ease;
    transition: all 0.3s ease;
    color: white;
    text-align: center;
   
}

    #return-to-top-Nht i {
        margin: 0;
        position: relative;
        left: 16px;
        top: 13px;
        font-size: 19px;
        -webkit-transition: all 0.3s ease;
        -moz-transition: all 0.3s ease;
        -ms-transition: all 0.3s ease;
        -o-transition: all 0.3s ease;
        transition: all 0.3s ease;
 
    }

    #return-to-top-Nht:hover {
        background: rgba(0, 0, 0, 0.8);
    }

        #return-to-top-Nht:hover i {
            color: #fff;
            top: 5px;
        }