:target

The :target pseudo-class represents the unique element, if any, with an id matching the fragment identifier of the URI of the document..

<!doctype html>
<html>
    <head>
        <title>:target pseudoclass example</title>
        <style type="text/css">
            #newcomment {
                display: none;
            } #newcomment:target {
                display: block;
            }
        </style>
    </head>
    <body>
        <p>
            <a href="#newcomment">Add a comment</a>
        </p>
        <div id="newcomment">
            <form name="myForm">
                <p>
                    Write your comment:
                    <br/>
                    <textarea name="myTextarea">
                    </textarea>
                </p>
            </form>
        </div>
    </body>
</html>