JS Hover Example

HTML

<script src="https://code.jquery.com/jquery-3.4.1.slim.js"></script>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.0/umd/popper.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.js"></script>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.css">
<!-- 
  Bootstrap docs: https://getbootstrap.com/docs
-->

<div class="container">
  <div class="row">
    <div class="col">
      <ul>
        <li id="prob1" onmouseover="mouse_over('.hover-class-1')" onmouseout="mouse_out('.hover-class-1')">Problem 1</li>
        <li id="prob2" onmouseover="mouse_over('.hover-class-2')" onmouseout="mouse_out('.hover-class-2')">Problem 2</li>
      </ul>
    </div>
    <div class="col">
      <table>
        <tr>
          <td class="hover-class-1 hover-class-2">A</td>
          <td class="hover-class-1">B</td>
        </tr>
        <tr>
          <td class="">C</td>
          <td class="hover-class-2">D</td>
        </tr>
      </table>
    </div>
  </div>  
</div>

CSS

.row {
  background: #f8f9fa;
  margin-top: 20px;
}

.col {
  border: solid 1px #6c757d;
  padding: 10px;
}

JavaScript

function mouse_over(aClass) {
  let elements_to_highlight = document.querySelectorAll(aClass);
  elements_to_highlight.forEach(el => {
    el.classList.add("bg-danger");
  });
}

function mouse_out(aClass) {
  let elements_to_highlight = document.querySelectorAll(aClass);
  elements_to_highlight.forEach(el => {
    el.classList.remove("bg-danger");
  });
}