偽元素 ::before 或 ::after 的使用

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偽屬性的區塊範圍如下範例

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">

    <style>

        p {
            border: 1px solid black;
            display: inline-block;
            width: 100px;
            color: blue;
            background: red;
        }

            p::before {
                content: 'before';
                background: green;
            }

            p::after {
                content: 'after';
                background: yellow;
            }
    </style>

</head>
<body>
    <div>
        <p>p1</p>
        <p>p2</p>
        <p>p3</p>
    </div>
    <div>
        <p>p1</p>
        <p>p2</p>
        <p>p3</p>
    </div>
</body>
</html>

 

偽元素的屬性可以部份相依於本體元素屬性，也可以替自己獨立指定屬性。

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width">

    <style>

        p {
            position: relative;
            border: 1px solid red;
            display: inline-block;
            width: 100px;
            color: blue;
        }

            p::before {
                content: 'before';
                color: green;
            }

            p::after {
                content: 'after';
                position: absolute;
                left: 10px;
            }
    </style>

</head>
<body>
    <div>
        <p>p1</p>
        <p>p2</p>
        <p>p3</p>
    </div>
    <div>
        <p>p1</p>
        <p>p2</p>
        <p>p3</p>
    </div>
</body>
</html>

如範例，

p tag 偽元素 after 的顏色不個別指定時，則相依於本體元素的藍色，

而 p tag 偽元素 after 的 position 屬性可自己獨立指定不同於本體的屬性值。