box-sizing的意义（两种区别） -

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>box-sizing的意义</title>
  </head>
  <style>
    .box1 {
      width: 200px;
      height: 200px;
      padding: 20px;
      margin: auto;
      box-sizing: content-box;
      background-color: darkslateblue;
    }
    .box2 {
      width: 200px;
      height: 200px;
      padding: 20px;
      margin: auto;
      box-sizing: border-box;
      background-color: rgb(169, 167, 187);
    }
  </style>
  <body>
    <div class="box1"></div>
    <div class="box2"></div>
  </body>
</html>
二者区别效果图：