.intoroduction {
  position: relative;
  max-width: 1000px;
  margin: 0 auto;
  text-align: center;
}

.intoroduction:before {
  content: "";
  position: absolute;
  top: 225px;
  right: -35px;
  width: 215px;
  height: 208px;
  background: url(../img/about/introduction/img_artset_01.png) no-repeat center center;
  background-size: contain;
  -webkit-animation: up_dwn_anm 2s ease-in-out infinite alternate;
          animation: up_dwn_anm 2s ease-in-out infinite alternate;
}

.intoroduction:after {
  content: "";
  position: absolute;
  top: 626px;
  left: -10px;
  width: 185px;
  height: 178px;
  background: url(../img/about/introduction/img_artset_02.png) no-repeat center center;
  background-size: contain;
  -webkit-animation: up_dwn_anm 2s ease-in-out .5s infinite alternate;
          animation: up_dwn_anm 2s ease-in-out .5s infinite alternate;
}

.intoroduction .intro_txt01 {
  margin-top: 33px;
}

.intoroduction .intro_txt02 {
  margin-top: 15px;
  font-size: 18px;
  line-height: 2.25;
  text-shadow: 0px 0px 4px #000, 0px 0px 5px #000, 0px 0px 10px #000;
}

.intoroduction .intro_txt03 {
  margin-top: 15px;
}

.story {
  margin-top: 48px;
  text-align: center;
}

.story .story_title {
  width: 654px;
  margin: 0 auto;
}

.story .story_txt {
  margin-top: 15px;
  font-size: 17px;
  line-height: 2.2;
  text-shadow: 0px 0px 4px #000, 0px 0px 5px #000, 0px 0px 10px #000;
}

@-webkit-keyframes up_dwn_anm {
  0% {
    -webkit-transform: translateY(0);
            transform: translateY(0);
  }
  100% {
    -webkit-transform: translateY(-5%);
            transform: translateY(-5%);
  }
}

@keyframes up_dwn_anm {
  0% {
    -webkit-transform: translateY(0);
            transform: translateY(0);
  }
  100% {
    -webkit-transform: translateY(-5%);
            transform: translateY(-5%);
  }
}

@media screen and (max-width: 767px) {
  .intoroduction {
    background: url(../img/common/bg_swirl_02.png) no-repeat left -25% bottom;
    background-size: 70% auto;
  }
  .intoroduction:before {
    top: auto;
    right: 5%;
    bottom: 3%;
    width: 127px;
    height: 125px;
  }
  .intoroduction:after {
    display: block;
    position: static;
    width: 110px;
    height: 106px;
    margin-top: 17%;
    margin-left: 8%;
  }
  .intoroduction .intro_txt01 {
    margin-top: 7%;
  }
  .intoroduction .intro_txt02 {
    margin-top: 4.5%;
    font-size: 13px;
    line-height: 2;
    letter-spacing: -.03em;
  }
  .intoroduction .intro_txt03 {
    margin-top: 4%;
  }
  .story {
    margin-top: 2%;
  }
  .story .story_title {
    width: 100%;
  }
  .story .story_txt {
    margin-top: 15px;
    font-size: 12px;
    line-height: 2;
  }
}