Q:

Unable to get menu to expand with expanding submenu

I'm having a difficult time getting an expanding menu to work. I have a need to have a menu that has items that has sub menu items. We don't want the sub menu items to always be displayed. The approach I want to use is to have and arrow (analogous to a + sign) to the left of the menu items that have sub menu items. I want the user to be able to select the arrow to display the sub menu items. The arrow will change direction (analogous to a - sign). My issue is not in getting the arrow and sub menus to show. My issue is in expanding the upper level div to show the sub menu items. (see sample)
#navigation_slideout {
  position: fixed;
  top: 85px;
  left: -370px;
  -webkit-transition-duration: .5s;
  -moz-transition-duration: .5s;
  -o-transition-duration: .5s;
  transition-duration: .5s;
  -webkit-border-radius: 5px;
  -moz-border-radius: 5px;
  border-radius: 5px;
  -webkit-box-shadow: 0 0 40px #222;
  -moz-box-shadow: 0 0 40px #222;
  box-shadow: 0 0 40px #222;
}
#navigation_slideout:hover {
  left: -39px;
}
#navigation_slideout ul {
  list-style: none;
}
#navigation_slideout ul li {
  background: #548EBE;
  width: 325px;
  height: 30px;
  text-align: left;
  padding-top: 5px;
  font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, sans-serif;
  font-size: 12pt;
  color: white;
  font-weight: bold;
}
#navigation_slideout ul li a {
  color: #000;
  text-decoration: none;
  font-weight: bold;
  display: block;
  background-color: #548EBE;
  color: white;
}
#navigation_slideout ul li ul {
  width: 285px;
}
#navigation_slideout ul li ul li {
  width: 10px;
  position: relative;
  left: -41px;
}
#navigation_slideout ul li ul li a {
  background: #548EBE;
  width: 326px;
  height: 30px;
  text-align: left;
  padding-top: 5px;
  font-family: helvetica, arial, sans-serif;
  font-size: 12pt;
  color: white;
  font-weight: bold;
}
#menu {
  -ms-transform: rotate(-90deg);
  -webkit-transform: rotate(-90deg);
  transform: rotate(-90deg);
  font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, sans-serif;
  font-size: 14pt;
  color: white;
  font-weight: bold;
  margin: 0px 0px 0px 0px;
  right: 0px;
  padding: 0px 0px 0px 0px
}
#menu a {
  font-size: 14pt;
  color: white;
  font-weight: bold;
  text-decoration: none;
}
table.nospacing {
  border-collapse: collapse;
  border-spacing: 0;
  table-layout: fixed;
}
table.nospacing th,
td {
  padding: 0;
}
.menu-col {
  max-width: 30px;
}
.expanding25 label {
  /*background-color: #AAAFAB;
    border-radius: 5px;
    color: white;
    */
  padding: 3px;
  padding-left: 25px;
}
.expanding25 li {
  margin: 2px 2px 2px 0;
  padding: 5px;
}
.expanding25 li > ul {
  left: -35px;
  position: relative;
  width: 100%
}
.expanding25 input[type=checkbox] {
  display: none;
}
.expanding25 input[type=checkbox] ~ ul {
  max-height: 0;
  max-width: 0;
  opacity: 0;
  overflow: hidden;
  white-space: nowrap;
  -webkit-transition: all 1s ease;
  -moz-transition: all 1s ease;
  -o-transition: all 1s ease;
  transition: all 1s ease;
}
.expanding25 input[type=checkbox]:checked ~ ul {
  max-height: 100%;
  max-width: 100%;
  opacity: 1;
}
.expanding25 input[type=checkbox] + label:before {
  transform-origin: 25% 50%;
  border: 8px solid transparent;
  border-width: 8px 12px;
  border-left-color: white;
  margin-left: -20px;
  width: 0;
  height: 0;
  display: inline-block;
  text-align: center;
  content: '';
  color: #AAAFAB;
  -webkit-transition: all .5s ease;
  -moz-transition: all .5s ease;
  -o-transition: all .5s ease;
  transition: all .5s ease;
  position: absolute;
  margin-top: 1px;
}
.expanding25 input[type=checkbox]:checked + label:before {
  transform: rotate(90deg);
  /*margin-top: 6px;
  margin-left: -25px;*/
}

<div id="navigation_slideout" style="background-color:#548EBE;z-index:1" onclick="">
  <table class="nospacing" style="border-style:none">
    <tr>
      <td>
        <ul>
          <li>&nbsp;&nbsp;&nbsp;Title</li>
          <li><a href="#">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Home</a>
          </li>
          <li><a href="#">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;About</a>
          </li>
          <li><a href="#">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Contacts</a>
          </li>
          <li><a href="#">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;FAQs</a>
          </li>
          <li class="expanding25">
            <input class="expanding25" type="checkbox" id="cb28" />
            <label class="expanding25" for="cb28">Topic Areas</label>
            <ul class="expanding25">
              <li class="expanding25">
                <label class="expanding25">Topic 1</label>Content</li>
              <li class="expanding25">
                <label class="expanding25">Topic 2</label>Content</li>
              <li class="expanding25">
                <label class="expanding25">Topic 3</label>Content</li>
              <li class="expanding25">
                <label class="expanding25">Topic 4</label>Content</li>
            </ul>
          </li>

        </ul>
      </td>
      <td class="menu-col" style="border-left:medium;border-left-color:white;border-left-style:solid">
        <p id="menu">MENU</p>
      </td>

    </tr>
  </table>

</div>

A:

All #navigation_slideout ul li are getting height: 30px, so your submenu is inside an li that can’t grow tall enough to show it. Adding this style will fix it:
#navigation_slideout ul li.expanding25 { height: auto }

Sample.

