:has(<direct-selector>) {

  /* ... */

}

const h1Elements = document.querySelectorAll('h1');

​

h1Elements.forEach((h1) => {

  const h2Sibling = h1.nextElementSibling;

  if (h2Sibling && h2Sibling.tagName.toLowerCase() === 'h2') {

    h1.classList.add('highlight-content');

  }

});

h1:has(+ h2) {

    color: blue;

}