.button_container {
  position: absolute;
  top: 0;
  right: 5%;
  height: 27px;
  width: 32px;
  cursor: pointer;
  z-index: 100;
  -webkit-transition: opacity .1s ease;
  transition: opacity .1s ease;
}
.button_container:hover {
  opacity: .375;
}
.button_container.active .top {
  -webkit-transform: translateY(11px) translateX(0) rotate(45deg);
          transform: translateY(11px) translateX(0) rotate(45deg);
}
.button_container.active .middle {
  opacity: 0;
}
.button_container.active .bottom {
  -webkit-transform: translateY(-11px) translateX(0) rotate(-45deg);
          transform: translateY(-11px) translateX(0) rotate(-45deg);
}
.button_container span {
  background: #000000;
  border: none;
  height: 2px;
  width: 100%;
  position: absolute;
  top: 0;
  left: 0;
  -webkit-transition: all .15s ease;
  transition: all .15s ease;
  cursor: pointer;
}
.button_container span:nth-of-type(2) {
  top: 11px;
}
.button_container span:nth-of-type(3) {
  top: 22px;
}
.overlay {
  position: fixed;
  background: #ffffff;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  opacity: 0;
  visibility: hidden;
  -webkit-transition: opacity .35s .35s, visibility .35s .35s;
  transition: opacity .35s .35s, visibility .35s .35s;
  overflow: hidden;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;  
}
.overlay.open {
  opacity: 1;
  visibility: visible;
  -webkit-transition: opacity .35s, visibility .35s;
  transition: opacity .35s, visibility .35s;
}
.overlay.open li {
  -webkit-animation: fadeIn .2s ease forwards;
          animation: fadeIn .2s ease forwards;
  -webkit-animation-delay: .2s;
          animation-delay: .2s;
}
.overlay nav {
  position: relative;
  height: 70%;
  top: 50%;
  -webkit-transform: translateY(-50%);
          transform: translateY(-50%);
  font-size: 1.75em;
  text-align: center;
}
.overlay ul {
  list-style: none;
  padding: 0;
  margin: 0 auto;
  position: relative;
  height: 100%;
}
.overlay ul li {
  height: 20%;
  height: calc(100% / 5);
  min-height: 40px;
  position: relative;
  margin-bottom: 0;
  line-height: 1;
  opacity: 0;
}
.overlay ul li a {
  position: relative;
  top: 50%;
  transform: translate(0,-50%);
  color: #000000;
  text-decoration: none;
  transition: opacity .1s linear;
  -webkit-backface-visibility: hidden;
}
.overlay ul li a:hover {
  opacity: 1.0;
}
@-webkit-keyframes fadeIn {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
@keyframes fadeIn {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}