@media (max-width:640px) {
  #logo {
    width: 75px;
  }

  #sidebar {
    position: relative;
    left: 0;
    width: 100%;
    padding-left: 1.75em;
  }

  #sidebar ul li {
    float: left;
    margin-right: 2em;
  }

  .footer {
    position: relative;
    top: 2em;
    clear: both;
  }

  #content {
    margin: 0;
  }
}