:first-child

Select and style every

element that is the first child of its parent:

<!DOCTYPE html>
<html>
    <head>
        <style>
            p:first-child {
                background-color: yellow;
            }
        </style>
    </head>
    <body>
        <p>
            This paragraph is the first child of its parent (body).
        </p>
        <h1>Welcome to My Homepage</h1>
        <p>
            This paragraph is not the first child of its parent.
        </p>
        <div>
            <p>
                This paragraph is the first child of its parent (div).
            </p>
            <p>
                This paragraph is not the first child of its parent.
            </p>
        </div>
        <p>
            <b>Note:</b>
            For :first-child to work in IE8 and earlier, a DOCTYPE must be 
declared.
        </p>
    </body>
</html>