问使用“对齐-内容:空格-环绕”行为展开框

EN

body {
  padding: 50px;
}
.parent {
  background: hsl(0,0%,90%);
  display: -webkit-flex;
  display:    -moz-flex;
  display:     -ms-flex;
  display:      -o-flex;
  display:         flex;
  -webkit-justify-content: space-around;
  -moz-justify-content: space-around;
  -ms-justify-content: space-around;
  -o-justify-content: space-around;
  justify-content: space-around;    
}
.child {
  background-color:blue;
  border: 1px solid hsl(0,0%,60%);
  padding: 20px;
  flex-grow: 1;
}

<div class="parent">
  <div class="child">this is a long text</div>
  <div class="child">2</div>
  <div class="child">3</div> 
</div>