<div class="parent">
<div class="child1">
</div>
</div>
.parent{
display:flex;
flex-direction:
row;
}
.child1{
width:100%; //这个无效
}//修改如下 parent加上 position: relative; 子加上 position: absolute;
.parent{
display:flex;
flex-direction:
row;
position:
relative
;
}
.child1{
position: absolute;
width:100%;
left:0;
top:0;
}