z-index는 position이 "> Document

z-index는 position이 ">
<aside> 💡
몇번 종이에 있을지를 결정하는 것!!
</aside>
<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <title>Document</title>
    <style>
      /* 깊이 1 */
      .box1 {
        width: 300px;
        height: 300px;
        background-color: yellow;
        display: inline-block;
      }

      /* 깊이 1 */
      .box2 {
        width: 300px;
        height: 300px;
        background-color: red;
        display: inline-block;
      }

      /* 깊이 1 */
      .box3 {
        width: 300px;
        height: 300px;
        background-color: green;
        display: inline-block;
      }

      /* 깊이 2 */
      .box4 {
        width: 300px;
        height: 300px;
        background-color: blue;
        display: inline-block;
        position: absolute;
        z-index: 99;
      }

      /* 깊이 1 */
      .box5 {
        width: 300px;
        height: 300px;
        background-color: bisque;
        display: inline-block;
        position: relative;
        z-index: 1;
      }
    </style>
  </head>
  <body>
    <h1>z-index는 position이 static이 아닌애들로만 작동한다</h1>
    <hr />
    <div class="box1"></div>
    <div class="box2"></div>
    <div class="box3"></div>
    <div class="box4"></div>
    <div class="box5"></div>
  </body>
</html>