Change “login/register” to “useraccount” when a user has logged in

I did a similar thing in many of my projects, here’s how I did it:

<div class="user-panel">
    <ul>
        <?php
        if (is_user_logged_in() ) {
            // When the user is Logged-in
            $current_user= wp_get_current_user();
            echo '<li>'. __( 'Welcome, ', 'text-domain' ) .'<strong>'. $current_user->user_nicename .'</strong></li>';
            echo '<li><a href="'. wp_logout_url( home_url() ) .'" title="Log out">'. __( 'Log out', 'text-domain' ) .'</a></li>';
        }
        else
        {
            // When user is logged-out
            echo '<li><a href="'. wp_registration_url() .'" title="Register a New Account">'. __( 'Register', 'text-domain' ) .'</a></li>';
            echo '<li><a href="'. wp_login_url() .'" title="Login to the site">'. __( 'Login', 'text-domain' ) .'</a></li>';
        } ?>
    </ul>
</div>
<!-- /.user-panel -->

It’s not a matter of CSS, it’s a matter of Templating. After this, do the CSS to make it look better. 🙂