<div class="demo">
<div class="first box">名稱只有 "first"</div>
    <div class="second box">名稱只有 "second"</div>
    <div class="first second box">名稱同時具有 "first" 和 "second" </div>
  
    <div class="first box">
        <div class="second">名稱為 "second"，階層於名稱為 "first" 的div之下 </div>
    </div>
  
    <div class="second box">
        <div class="first">名稱為 "first" ，階層位於名稱為 "second" 的div之下 </div>
    </div>
</div>
/* 指定 first 裡面的 second 才會顯示黑色*/
.first .second{
    background-color: black;
    color: white;
    height: auto;
}


/* CSS For Decoration */
html, body{
    font-family: "微軟正黑體";
    font-weight: bold;
}
.demo{
    display:  ;
    height: 50vh;
    justify-content: space-around;
}
.box{
    width: 150px;
    height: 70px;
    margin: auto;
    border: 2px solid #000;
    border-radius: 5px;
    text-align: left;
    padding: 10px;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.