Detailed explanation of the solution for HTML layout with fixed left and right widths and adaptive middle

<div class="box">
    <div class="left">left</div>
    <div class="right">right</div>
    <div class="center">center</div>
</div>   
//Note here that the left and right floating elements should be rendered first, and then the middle element. After the element is floated, the remaining sibling block-level elements will occupy the width of the parent element <style>
   .box{
        height:200px;
    }    
    .left{
        float:left;
        width:300px;
    }
    .right{
        float:right;
        width:300px;
    }
</style>

<div class="box">
    <div class="left">left</div>
    <div class="right">right</div>
     <div class="center">center</div>
</div> 
//Similar to the floating layout, render the left and right elements first, so that they are positioned at the left and right ends of the parent element, and the remaining middle elements occupy the remaining width of the parent element.
<style>
    .box{
        position: relative;
      }
      .left{
        position: absolute;
        width: 100px;
        left: 0;
      }
      .right{
        width:100px;
        position: absolute;
        right: 0;
      }
      .center{
        margin: 0 100px;
        background: red;
      }
</style>

<div class="box">
  <div class="left">
    left
  </div>
  <div class="center">
    center
  </div>
  <div class="right">
    right
  </div>
</div>
<style>
    .box{
        display: table;
        width: 100%;
      }
      .left{
        display: table-cell;
        width: 100px;
        left: 0;
      }
      .right{
        width:100px;
        display: table-cell;
      }
      .center{
        width: 100%;
        background: red;
      }
</style>

<div class="box">
  <div class="left">
    left
  </div>
  <div class="center">
    center
  </div>
  <div class="right">
    right
  </div>
</div>
<style>
    .box{
        display: flex;
        width: 100%;
      }
      .left{
      
        width: 100px;
        left: 0;
      }
      .right{
        width:100px;
      }
      .center{
        flex:1;
      }
</style>

<div class="box">
  <div class="left">
    left
  </div>
  <div class="center">
    center
  </div>
  <div class="right">
    right
  </div>
</div>
<style>
  .box{
        display: grid;
        grid-template-columns: 100px auto 100px;
        width: 100%;
      }
</style>