.

 Add this to the functions.php file of your active theme to inject custom CSS to the admin area of your site.

add_action('admin_head', 'my_custom_admin_css');

function my_custom_admin_css() {
  echo '<style>
    body, td, textarea, input, select {
      font-family: "Lucida Grande";
      font-size: 12px;
    } 
  </style>';
}