Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="dropdown">
    <input type="checkbox" id="dropdownToggle" />
    <label for="dropdownToggle">DROPDOWN</label>
    <ul class="dropdown-menu">
       <li>List Item</li> 
       <li>List Item</li>
    </ul>
</div>

SassMeister-input.scss

// ----
// Sass (v3.4.12)
// Compass (v1.0.3)
// ----

.dropdown {
  #dropdownToggle {
    display:none;
    &:checked ~ .dropdown-menu {
      display: block;
    }
  }
  
  .dropdown-menu {
    display: none;
  }
}

SassMeister-output.css

.dropdown #dropdownToggle {
  display: none;
}
.dropdown #dropdownToggle:checked ~ .dropdown-menu {
  display: block;
}
.dropdown .dropdown-menu {
  display: none;
}

SassMeister-rendered.html

<div class="dropdown">
    <input type="checkbox" id="dropdownToggle" />
    <label for="dropdownToggle">DROPDOWN</label>
    <ul class="dropdown-menu">
       <li>List Item</li> 
       <li>List Item</li>
    </ul>
</div>