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<input type="checkbox" id="toggle">
<label for="toggle">&#9776;</label>
<nav>
  <ul>
    <li><a href="#">Главная</a></li>
    <li><a href="#">О нас</a></li>
    <li><a href="#">Услуги</a></li>
    <li><a href="#">Контакты</a></li>
  </ul>
</nav>
body {
  font: 14px/24px "Open Sans", "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", Sans-Serif;
}
input {
  display: none;
}
label,
ul {
  border: 1px solid #cecfd5;
  border-radius: 6px;
}
label {
  color: #0087cc;
  cursor: pointer;
  display: inline-block;
  font-size: 18px;
  padding: 5px 9px;
  transition: all .15s ease;
}
label:hover {
  color: #ff7b29;
}
input:checked + label {
  box-shadow: inset 0 1px 2px rgba(0, 0, 0, 0.15);
  color: #9799a7;
}
nav {
  max-height: 0;
  overflow: hidden;
  transition: all .15s ease;
}
input:checked ~ nav {
  max-height: 500px;
}
ul {
  list-style: none;
  margin: 8px 0 0 0;
  width: 100px;
}
li {
  border-bottom: 1px solid #cecfd5;
}
li:last-child {
  border-bottom: 0;
}
a {
  color: #0087cc;
  display: block;
  padding: 6px 12px;
  text-decoration: none;
}
a:hover {
  color: #ff7b29;
}