因此,只有当页面滚动时,已转换的元素才能越过固定栏,其他元素则不会.那么问题是转化元素是否具有默认的z-index？

When you use z-index: -1; for .transform_me it behaves normal

Demo

CSS

.fixed {
    height: 30px;
    background: #f00;
    position: fixed;
    width: 100%;
    top: 0;
}

.transform_me {
    transform: rotate(360deg);
    -webkit-transform: rotate(360deg);
}

span {
    display: block;
    height: 100px;
}

Note: It will be solved if we use say z-index: 999; for the fixed
div,but that’s not what am looking for.