(2019)[前端]面试题[3]：三大定位，相对定位放在固定定位产生什么影响？

<div class="parent">
    <div class="child">child</div>
</div

<style>
    .parent {
        margin-top: 100px;
        position: fixed;
        top: 0;
        left: 0;
        width: 300px;
        background-color: #eee;

    }

    .child {
        height: 20px;
        width: 120px;
        background-color: red;
    }
</style>

.child {

    position: fixed;
    top: 0;
    left: 0;
    height: 20px;
    width: 120px;
    background-color: red;
}