很明显右边空出太多留白了

<div class="list1">
    <div class="list2">
        <div class="item">优酷</div>
        <div class="item">爱奇艺</div>
        <div class="item">腾讯</div>
        <div class="item">芒果</div>
        <div class="item">土豆</div>
    </div>
</div>

.list1{
    display: flex;
    justify-content: center;
    .list2{
        display: flex;
        flex-wrap: wrap;
    }
    .item{
        width: 100px;
        text-align: center;
        padding: 6px 0;
        border: 1px solid #dedede;
        margin: 4px;
    }
}

让子元素整体居中，这该怎么实现呀？

你的父盒子应该定义宽度啊，不然父元素只是被里面的元素撑开了而已，达不到你要的效果。把list2的宽度设为试试看？

.list1{

    display: flex;
    justify-content: center;
    }
.list2{
    width: ; 
    /* 要加宽度 */
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    /* 或者 justify-content:space-around */
}
.item{
    width: 100px;
    text-align: center;
    padding: 6px 0;
    border: 1px solid #dedede;
    margin: 4px;
}