<h2>Выберите навыки для жены (не более трех)</h2><hr>
     <div id="skills">
         <input type="checkbox" id="a" class="inp"><label for="a">Стирать</label><div>
             <input type="checkbox" id="b" class="inp"><label for="b">Готовить</label><div>
                 <input type="checkbox" id="c" class="inp"><label for="c">Рожать</label><div>
                     <input type="checkbox" id="d" class="inp"><label for="d">Думать</label><div>
                         <input type="checkbox" id="e" class="inp"><label for="e">Пить кровь</label><div>
                             <input type="checkbox" id="f" class="inp"><label for="f">Плакать</label><div></div>
                         </div>
          
                     </div>
          
                 </div>
          
             </div>
          
         </div>
          
     </div>

<style>
         #skills{
         position: relative;
         width: 200px}
          
         #skills i{
         }
          
         #skills .inp{
         float: left;
         margin:3px 10px}
          
         #skills label{
         display: block;
         margin:10px}
          
         .inp:checked,
         .inp:checked+label{
             position: relative;
             z-index:5}
          
         .inp:checked~div .inp:checked~div .inp:checked~div:before{
             content: '';
             position: absolute;
             top: 0;
             left: 0;
             z-index:1;
             display: block;
             width: 100%;
             height:100%;
             background:rgba(255,255,255,.5)
         }
     </style>

.inp:checked~div .inp:checked~div .inp:checked~div:before