知识点1:
默认后代选择器(儿子孙子)
>子代选择器(儿子)
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .c1 .c2{
            color: red;
        }
        .c1 p{
            color: green;
        }
        .c1 .c3 .c4{
            color: yellow;
        }
        .c1 .c5{
            color: pink;
        }
        .c1 > .c6{
            color: blue;
        }
    </style>
</head>
<body>
<div class="c1">
    <div class="c2">div1</div>
    <div class="c2">div11</div>
    <div class="c6">div111</div>
    <p>p1</p>
    <p>p2</p>
    <div class="c3">
        <div class="c4">div3</div>
        <div class="c5">div4</div>
        <div class="c6">div111</div>
        <p>p3</p>
        <p>p4</p>
    </div>
</div>
<div class="c1">div2</div>
<div class="c2">div3</div>
</body>
</html>
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