@import url(https://fonts.googleapis.com/css?family=Bitter);
body {
  margin: 0;
  font-family: "Bitter", serif;
  text-align: center;
}
.holder,
.first,
.second,
.third {
  height: 100vh;
  width: 100vw;
}
.first,
.second,
.third {
  position: absolute;
}
.second,
.third {
  opacity: 0;
}
.holder {
  height: 100vh;
  position: relative;
  z-index: 1;
}
.first {
  animation: first 10s infinite;
  background: linear-gradient(#5ff8ca, #60e08c);
  z-index: 10;
}
@keyframes first {
  0% {
    opacity: 1;
  }
  10% {
    opacity: 0.8;
  }
  20% {
    opacity: 0.6;
  }
  30% {
    opacity: 0.4;
  }
  40% {
    opacity: 0.2;
  }
  50% {
    opacity: 0.1;
  }
  60% {
    opacity: 0.2;
  }
  70% {
    opacity: 0.4;
  }
  80% {
    opacity: 0.6;
  }
  90% {
    opacity: 0.8;
  }
  100% {
    opacity: 1;
  }
}

.second {
  animation: second 10s infinite;
  animation-delay: 2s;
  background: linear-gradient(#19eaa6, #00a1f0);
  z-index: 20;
}
@keyframes second {
  0% {
    opacity: 0;
  }
  10% {
    opacity: 0.2;
  }
  20% {
    opacity: 0.4;
  }
  30% {
    opacity: 0.6;
  }
  40% {
    opacity: 0.8;
  }
  50% {
    opacity: 1;
  }
  60% {
    opacity: 0.8;
  }
  70% {
    opacity: 0.6;
  }
  80% {
    opacity: 0.4;
  }
  90% {
    opacity: 0.2;
  }
  100% {
    opacity: 0;
  }
}

.third {
  animation: third 10s infinite;
  animation-delay: 8s;
  background: linear-gradient(#aab7f8, #ff75c6);
  z-index: 30;
}
@keyframes third {
  0% {
    opacity: 0;
  }
  10% {
    opacity: 0.2;
  }
  20% {
    opacity: 0.4;
  }
  30% {
    opacity: 0.6;
  }
  40% {
    opacity: 0.8;
  }
  50% {
    opacity: 1;
  }
  60% {
    opacity: 0.8;
  }
  70% {
    opacity: 0.6;
  }
  80% {
    opacity: 0.4;
  }
  90% {
    opacity: 0.2;
  }
  100% {
    opacity: 0;
  }
}

.txt {
  margin-top: calc(50vh - 43px);
  position: absolute;
  width: 100%;
  z-index: 1000;
}

.content {
  background-color: rgba(255, 255, 255, 0.557);
  border-radius: 0.25em;
  box-shadow: 0 0 0.25em rgba(0, 0, 0, 0.25);
  box-sizing: border-box;
  left: 50%;
  padding: 10vmin;
  position: fixed;
  text-align: center;
  top: 50%;
  transform: translate(-50%, -50%);
}

h1 {
  font-family: serif;
}

.title_1 {
  font-weight: bold;
  font-size: 2rem;
}

.btn04 {
  color: #fff;
  font-size: 2rem;
  text-decoration: seashell;
  text-align: center;
  position: relative;
  z-index: 10;
  display: block;
  width: 150px;
  height: 150px;
  line-height: 150px;
  margin-left: 60px;
}

.btn04::before {
  content: "";
  background-color: #dda284;
  display: block;
  position: absolute;
  width: 150px;
  height: 150px;
  z-index: -1;
  border-radius: 50%;
  box-shadow: 0 0 0 0 #fff, 0 0 0 0 #dda284;
  transition: all 0.2s ease;
  -webkit-transition: all 0.2s ease;
}
.btn04:hover::before {
  transform: scale(0.8);
  -webkit-transform: scale(0.8);
  box-shadow: 0 0 0 25px #fff, 0 0 0 27px #dda284;
}

.button {
  color: #fff;
  background: #ec16c1;
  font-size: 16px;
  border-radius: 4px;
  text-decoration: none;
  padding: 1em 3em;
  display: inline-block;
}
/* 光らせるためのstyle */
.shine {
  border: 2px solid transparent;
  position: relative;
  overflow: hidden;
}
/* 光の疑似要素 */
.shine::before {
  content: "";
  animation: shine 3s cubic-bezier(0.25, 0, 0.25, 1) infinite;
  background-color: #fff;
  width: 140%;
  height: 100%;
  transform: skewX(-45deg);
  top: 0;
  left: -160%;
  opacity: 0.5;
  position: absolute;
}
/* 光の動き */
@keyframes shine {
  0% {
    left: -160%;
    opacity: 0;
  }
  70% {
    left: -160%;
    opacity: 0.5;
  }
  71% {
    left: -160%;
    opacity: 1;
  }
  100% {
    left: -20%;
    opacity: 0;
  }
}