.but_body_backstretch { position: fixed; top: 48%; border: 1px #FFF solid; background: #000; margin:0.5rem;
                        -moz-border-radius: 2rem; /* Firefox */
                        -webkit-border-radius: 2rem; /* Safari and Chrome */
                        border-radius: 2rem;
                        opacity: 0.4;}
.but_body_backstretch span { padding: 0.2em; display: block; width: 2em; text-align: center; color: #FFF; line-height: 1.5em; margin: 0px; height: 2em; font-size: 1em; }
.but_body_backstretch.nav_next { right: 1rem; }
.but_body_backstretch.nav_prev { left: 1rem; }
.but_body_backstretch:hover { opacity: 0.8; background: #FFF; border-color: #000; }
.but_body_backstretch:hover span { color: #000; }