Check this fiddle
I have a dropdown and when the dropdown is toggled, I want to change  another div's background-color (div's with classes .main-content and .reqdiv is this case).
I have tried these selectors ~, >, + and I know these won't work in my case. Can anyone please suggest me how to solve this without using JS/JQuery.
.main-content {
  height: 200px;
  width: 100%;
  background: green;
}
.dropdown-menu {
  top: 35px!important;
}
.nav-btn.show~.main-content {
  background: blue;
}
.nav-btn.show>.main-content {
  background: blue;
}
.nav-btn.show+.main-content {
  background: blue;
}<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" rel="stylesheet" />
<div class="row">
  <div class="nav-btn">
    <button class="btn dropdown-toggle " type="button" data-toggle="dropdown"><b>Language</b>
   <span class="caret"></span>
   </button>
    <ul class="dropdown-menu">
      <li><a href="#">HTML</a>
      </li>
      <li><a href="#">CSS</a>
      </li>
      <li><a href="#">JavaScript</a>
      </li>
    </ul>
  </div>
</div>
<div class="#reqdiv">
  //text
</div>
<div class="main-content">
</div> 
     
     
    