05justify-content

display: flex; 的默认轴是x轴
justify-content: 设置主轴上的子元素排列的方式
所以在使用之前要确定好哪一个是主轴

/* justify-content:flex-start; 如果主轴是x,从左到右 如果主轴是y,从上到下*/
/* justify-content: flex-end; 如果主轴是y,从下到上到右 如果主轴是x,从右到做*/
/* justify-content:center; 居中*/
/* justify-content: space-around; */
/* justify-content: space-between; */

#main {
    width: 800px;
    height: 300px;
    border: 1px solid #c3c3c3;
    display: flex;
    flex-direction: row;
    justify-content:flex-start;
}

#main>div{
    width: 150px;
    height: 100px;
    background: #0099FF;
}

<div id="main">
  <div style="background-color:coral;">11</div>
  <div style="background-color:lightblue;">22</div>
  <div style="background-color:pink;">33</div>
  <div style="background-color:olive;">4</div>
</div>

justify-content:flex-end;

justify-content: space-around;