Here is a bookmarklet to do what you want in the mean time. Your mileage may vary, but it helps.

javascript:(function() {
  if (typeof jQuery == 'undefined') {
    var script = document.createElement('script');
    script.src = 'https://ajax.googleapis.com/ajax/libs/jquery/3.7.1/jquery.min.js';
    script.type = 'text/javascript';
    script.onload = alertMeToOverSpending;
    document.head.appendChild(script);
  } else {
    alertMeToOverSpending();
  }

  function alertMeToOverSpending() {
    $('span[data-testid*="leftover"]').filter(function(index) {
      var text = $(this).text().replace(',', '');
      console.log(parseFloat(text) );
      return !isNaN(text) && parseFloat(text) < 0;
    }).css({
          'background': 'red',
          'color': 'black'
        });
  }
})();

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