我有一个名为.side-el的div，我希望它的位置是:Fixed；Behavior，但是一旦我应用了位置固定，宽度就会从右边交替.正确的宽度将是由FlexBox设置的宽度.我怎样才能达到这个目标呢？
.container {
-webkit-align-content: flex-start;
align-content: flex-start;
-webkit-align-items: flex-start;
align-items: flex-start;
display: -webkit-flex;
display: flex;
-webkit-flex-direction: row;
flex-direction: row;
-webkit-flex-wrap: wrap;
flex-wrap: wrap;
-webkit-justify-content: flex-start;
justify-content: flex-start;
* {
box-sizing: border-box;
-webkit-flex-grow: 1;
flex-grow: 1;
-webkit-flex-shrink: 0;
flex-shrink: 0;
}
}
.main-el {
box-sizing: border-box;
padding:0 2em;
width: 70%;
}
.side-el {
box-sizing: border-box;
width: 30%;
}<div class="container" style="background-color: blue; height: 100px;">
<div class="main-el">
<div style="background-color: red; height: 1000px;">content</div>
</div>
<div class="side-el" >
<div style="background-color: red; height: 100px;">content</div>
</div>
</div>