nutui/sites/doc/compents/backtop/backtop.scss

.nut-backtop {
    display: none;
    line-height: 0;
    position: fixed;
    cursor: pointer;
    bottom: 20px;
    right: 10px;
    z-index: 1111;
    &.show {
        display: block;
    }
    &-main {
        transition: all .2s ease-in-out;
        width: 38px;
        height: 38px;
        background: #FFF url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 31 39'%3E%3Cg fill-rule='evenodd'%3E%3Cpath d='M1.41 0C.63 0 0 .672 0 1.5S.63 3 1.41 3h28.18C30.37 3 31 2.328 31 1.5S30.369 0 29.59 0H1.41zM17 7.5a1.5 1.5 0 0 0-3 0v30a1.5 1.5 0 1 0 3 0v-30zM8.44 12.44l-8 8a1.5 1.5 0 1 0 2.12 2.12l8-8a1.5 1.5 0 1 0-2.12-2.12z'/%3E%3Cpath d='M16.56 6.44l14 14a1.5 1.5 0 1 1-2.12 2.12l-14-14a1.5 1.5 0 1 1 2.12-2.12z'/%3E%3C/g%3E%3C/svg%3E") no-repeat center;
        background-size: 20px 20px;
        border-radius: 50%;
        border: 2px solid rgba(180,180,180,.5);
        box-shadow: 0px 0px 2px 3px rgba(220, 220, 220, .1)
    }
    i {
        color: #fff;
        font-size: 24px;
        padding: 8px 12px;
        line-height: 0;
    }
}