#center{
    text-align: center;
}
#back{
    width: 200px;
    height: 251px;
    opacity: .5;
    background-image: url('portfolio_project-images/small_img_back.png');
    display: inline-block;
    
}

#back:hover {
    width: 200px;
    height: 251px;
    opacity: 1;
    cursor: pointer;
    background-image: url('portfolio_project-images/small_img_hover_back.png');
}


#footer {
    width: 120px;
    height: 74px;
    opacity: .5;
    background-image: url('portfolio_project-images/image_page/img_foot.png');
    margin-top: 300px;
    display: inline-block;
    
}

#footer:hover {
    opacity: 1;
    cursor: pointer;
}