3.9 结合使用 CSS

通过 JavaScript 修改 CSS 属性；

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <style>
        .myStyle {
            background-color: red;
        }
    </style>
</head>
<body>
<p id="p">JavaScript</p>
<button onclick="changeColoe()">点击说话</button>
<script>
    function changeColoe() {
        document.getElementById("p").className = "myStyle";
    }
</script>
</body>
</html>