Answers for "css change parent onhover of child"

how to select child when hover on parent element css

/* Selecting a child element on :hover parent element*/ 
.parent:hover .child {
   /* ... */
}

change parent div css on over of child

<ul id="main-menu">
  <li>
    <a href="#">
      <i class="fa fa-building-o" aria-hidden="true"></i>
      Private Limited
      <i class="fa fa-caret-down"></i>
    </a>
    <ul class="submenu">
      <li><a href="#0">Company</a>
      </li>
      <li><a href="#0">Contact</a>
      </li>
      <li><a href="#0">Industry</a>
      </li>
    </ul>
  </li>
</ul>