Mutation events like DOMAttrModified are deprecated. Consider using a MutationObserver instead.
Example:
<div>use devtools to change the <code>background-color</code> property of this node to <code>red</code></div>
<p>status...</p>
JS:
var observer = new MutationObserver((mutations) => {
  mutations.forEach((mutation) => {
    if (mutation.target.style.color === 'red') {
      document.querySelector('p').textContent = 'success';
    }
  });
});
var observerConfig = {
  attributes: true,
  childList: false,
  characterData: false,
  attributeOldValue: true
};
var targetNode = document.querySelector('div');
observer.observe(targetNode, observerConfig);