@-webkit-keyframes btn-wake {
  0% {
    opacity: 1;
  }
  50% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
@keyframes btn-wake {
  0% {
    opacity: 1;
  }
  50% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
body {
  margin: 0;
  padding: 0;
  background:rgba(255, 255, 255, 0);
  background-size:cover;
  /*background-color: pink;*/
  font-family: helvetica, arial, sans-serif;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  width: 100vw;
}

header {
  color: #fff;
  position: fixed;
  width: 100%;
  bottom: 13vh;
  text-align: center;
  z-index: 98;
}
header h1 {
  font-family: "Abril Fatface", georgia, times, serif;
  font-size: 4rem;
  line-height: 4rem;
  margin: 0;
  padding: 0;
}
header small {
  font-size: 0.6rem;
  line-height: 0.6rem;
  margin: 0.6rem 0;
  letter-spacing: 0.05em;
  display: block;
}
header a {
  color: #222;
  text-decoration: none;
}

nav {
  display: flex;
  justify-content: center;
  align-items: center;
  z-index: 99;
  position: fixed;
  top: 0;
  left: 0;
  height: 100vh;
  width: 100vw;
}
nav a {
  font-family: arial;
  color: #222;
  border: 2px solid #222;
  padding: 10px 15px;
  transition: 100ms ease all;
  text-decoration: none;
  background: #fffeab;
}
nav a.wake {
  -webkit-animation-fill-mode: forwards;
          animation-fill-mode: forwards;
  -webkit-animation-iteration-count: 2;
          animation-iteration-count: 2;
  -webkit-animation-timing-function: ease;
          animation-timing-function: ease;
  -webkit-animation-duration: 0.5s;
          animation-duration: 0.5s;
  -webkit-animation-name: btn-wake;
          animation-name: btn-wake;
  -webkit-animation-delay: 1s;
          animation-delay: 1s;
}
nav a.disable {
  opacity: 1;
}
nav a.disable:hover {
  background: #fffeab;
}
nav a.disable:active {
  background: #fffeab;
}
nav a:hover {
  background: #fff;
}
nav a:active {
  background: #fffeab;
}
nav a + a {
  margin-left: 75vw;
}

section {
  width: 500px;
  height: 500px;
  min-width: 500px;
  margin: 0 auto;
  border-radius: 50%;
  overflow: hidden;
  position: relative;
  z-index: 1;
 opacity: 0.7;
}
section .layer {
  display: flex;
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}
section .layer:nth-child(1) {
  z-index: 4;
}
section .layer:nth-child(2) {
  z-index: 3;
}
section .layer:nth-child(3) {
  z-index: 2;
}
section .layer:nth-child(4) {
  z-index: 1;
}
section .layer.image-1 .slice.left .inner, section .layer.image-1 .slice.right .inner {
  background-image: url("../img/001.jpg");
  background-color: #6fb4c4;
}
section .layer.image-2 .slice.left .inner, section .layer.image-2 .slice.right .inner {
  background-image: url("../img/002.jpg");
  background-color: #d25223;
}
section .layer.image-3 .slice.left .inner, section .layer.image-3 .slice.right .inner {
  background-image: url("../img/003.jpg");
  background-color: #fec763;
}
section .layer.image-4 .slice.left .inner, section .layer.image-4 .slice.right .inner {
  background-image: url("../img/004.jpg");
  background-color: #a52a2c;
}
section .layer .slice {
  width: 50%;
  height: 100%;
  overflow: hidden;
}
section .layer .slice.left .inner, section .layer .slice.right .inner {
  width: 100%;
  height: 100%;
}
section .layer .slice.left.next, section .layer .slice.right.next {
  transform: rotate(180deg);
}
section .layer .slice.left.next .inner, section .layer .slice.right.next .inner {
  transform: rotate(-180deg);
}
section .layer .slice.left.prev, section .layer .slice.right.prev {
  transform: rotate(-180deg);
}
section .layer .slice.left.prev .inner, section .layer .slice.right.prev .inner {
  transform: rotate(180deg);
}
section .layer .slice.left, section .layer .slice.left .inner {
  transform-origin: 100% 50%;
  background-position: 0 50%;
}
section .layer .slice.right, section .layer .slice.right .inner {
  transform-origin: 0 50%;
  background-position: 100% 50%;
}
section .layer .slice.spin-in {
  transition: all 400ms ease-in;
}
section .layer .slice.spin-in .inner {
  transition: all 400ms ease-in;
}
section .layer .slice.spin-out {
  transition: all 400ms ease-out;
}
section .layer .slice.spin-out .inner {
  transition: all 400ms ease-out;
}