Change CSS when user is logged in

In your child-theme‘s functions.php, paste the following code:

add_action('wp_head', 'add_css_head');
function add_css_head() {
     if ( is_user_logged_in() ) { 
     ?>
          <style>
               .sellertitle {
                    float: left;
                    width: 49%;
               }
          </style>
     <?php
     } else {
     ?>
          <style>
               .sellertitle {
                    float: none;
                    width: 49%; }
          </style>
     <?php
     }
}

Change the CSS as needed.

Source: https://wordpress.stackexchange.com/questions/181630/change-css-when-user-is-logged-in