Add CSS to Admin side

functions.php

<?php

add_action('admin_head', 'custom_admin_css');

function custom_admin_css() {
  echo '<style>
    #the-list tr.status-wc-cancelled {
      background-color: #FCACAC;
    }
    #the-list tr.status-wc-completed {
      background-color: #ACFCFC;
    }
  </style>';
}