nutui/src/packages/backtop/backtop.scss

.nut-backtop{
    z-index: 1111;
    position: fixed;
    cursor: pointer;
    display: none;
    line-height: 0;
    &.show {
        display: block;
    }

    &-main {
        background-color: rgba(0,0,0,.3);
        border-radius: 2px;
        box-shadow: 0 1px 3px rgba(0,0,0,.2);
        transition: all .2s ease-in-out;
        
        &:hover {
            background-color: rgba(0,0,0,.5);
        }
    }

    i{
        color: #fff;
        font-size: 24px;
        padding: 8px 12px;
        line-height: 0;
    }
}