.back-to-top {
position: fixed; left: 50%; margin-left: 580px; bottom: 37px; background-color: #f8f8fd; visibility: hidden; opacity: 0; transition: 0.4s ease; box-shadow: 0 1px 3px 1px rgba(0, 0, 0, 0.3), 0 0 30px rgba(10, 10, 0, 0.1) inset; a { display: block; background-color: #eee; width: 38px; height: 38px; line-height: 38px; text-align: center; font-size: 20px; color: #b4b4b4; }
} .back-to-top-show{
visibility: visible; opacity: 0.7; &:hover{ opacity: 1 }
} @media screen and (max-width:1200px) and (min-width: 770px) {
.back-to-top { left: 50%; margin-left: 45.5%; }
} @media screen and (max-width: 770px) {
.back-to-top { right:2.5%; left: auto; // left: 50%; margin-left: 0px; a { width: 33px; height: 33px; line-height: 33px; text-align: center; font-size: 18px; } }
}