要设置作为其父级第一个子级的每个<p>元素的样式，请使用CSS：first-child选择器。
您可以尝试运行以下代码来实现：first-child选择器-
<!DOCTYPE html>
<html>
<head>
<style>
p:first-child {
background-color: orange;
}
</style>
</head>
<body>
<h1>Heading</h1>
<p>This is demo text.</p>
<div>
<p>This is demo text, with the first child of its parent div.</p>
<p>This is demo text, but not the first child.</p>
</div>
</body>
</html>