如果任何标记被突出显示，并且它们都需要被突出显示，这是一个简单的has（）调用。

ul:has(mark:hover) mark {
  background-color: red;
}

<ul>
  <li><span>First bullet </span><mark>point</mark></li>
  <li><mark>Second bullet</mark><span> point</span></li>
  <li><span>Third bullet </span><mark>point</mark></li>
  <li><mark>Fourth bullet</mark><span> point</span></li>
  <li><span>The </span><mark>Fifth bullet</mark><span> point</span></li>
</ul>

如果它适用的话，它只是围绕它的 Package 有点复杂
一个二个一个一个
仅仅使用JavaScript

const ul = document.querySelector("ul");

const removeActive = function (evt) {
  const active = evt.currentTarget.querySelector("mark.active");
  if (active) active.classList.remove("active");
}

ul.addEventListener("mouseover", function (evt) {
  removeActive(evt);
  let elem = null;

  const mark = evt.target.closest("mark");
  if (!mark) return;
  
  const li = mark.closest("li");
  
  if (!mark.previousSibling) {
    const prevLi = li.previousElementSibling;
    elem = prevLi && prevLi.lastChild;
  } else if (!mark.nextSibling) {
    const nextLi = li.nextElementSibling;
    elem = nextLi && nextLi.firstChild;
  }
  
  if (elem && elem.nodeName == "MARK") {
    elem.classList.add("active");
  }
});

ul.addEventListener("mouseleave", removeActive);

li mark:hover,
li mark.active {
  background-color: red;
}

<ul>
  <li>First bullet <mark>point</mark></li>
  <li><mark>Second bullet</mark> point</li>
  <li>Third bullet <mark>point</mark></li>
  <li><mark>Fourth bullet</mark> point</li>
  <li>The </span><mark>Fifth bullet</mark><span> point</li>
</ul>