.middle-menu {
  display: flex;
  justify-content: space-around;
  flex-wrap: wrap;
  align-items: end;
  padding: 30px 0;
}
.middle-menu a {
  width: 20%;
}
.middle-menu .middle-menu-item {
  position: relative;
  box-sizing: border-box;
  width: 100%;
  font-size: 18px;
  color: #000;
  text-align: center;
  transition: all 0.3s;
  perspective: 800px;
}

.middle-menu .middle-menu-item .middle-logo {
  transform-style: preserve-3d;
  transform-origin: center center;
}

.middle-menu .middle-menu-item:hover .middle-logo {
  animation: middle-logo-flip 0.8s linear;
}

@keyframes middle-logo-flip {
  0% {
    transform: rotateY(0deg);
  }
  45% {
    transform: rotateY(90deg);
  }
  50% {
    transform: rotateY(180deg);
  }
  55% {
    transform: rotateY(270deg);
  }
  100% {
    transform: rotateY(360deg);
  }
}

.middle-menu .middle-menu-item .middle-logo img {
  width: 60%;
  height: auto;
  margin: 0 auto;
  display: block;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}
.item-title {
  margin-top: 10px;
  color: #235D5E;
  font-weight: bold;
}
.item-title-en {
  margin-top: 5px;
  font-size: 14px;
  color: #999999;
}

.welcome-box-bg{
  background:url(../images/wel_bg.png) no-repeat right -1vw top -5vw,
  url(../images/wel_bg.png) no-repeat left 6vw bottom -6vw;
  background-size: 500px auto, 500px auto;
}
.welcome-box {
  padding: 30px 0;
}

.welcome-title {
  font-size: 42px;
  font-weight: bold;
  color: #235D5E;
  text-align: center;
  letter-spacing: 5px;
}

.welcome-title-cn {
  font-size: 24px;
  /* font-weight: bold; */
  color: #235D5E;
  text-align: center;
  margin: 5px auto 20px;
}
.welcome-content {
  font-size: 16px;
  color: #333333;
  line-height: 1.7;
  margin-bottom: 15px;
  text-align: justify;
}
.welcome-content-item {
  margin-bottom: 10px;
}
.welcome-content-item-en {
  font-family: "Arial", sans-serif;
  margin-bottom: 10px;
}
@media (max-width: 1600px) {
  .welcome-box-bg{
    background:url(../images/wel_bg.png) no-repeat right -3vw top -3vw,
    url(../images/wel_bg.png) no-repeat left 0vw bottom -7vw;
    background-size: 29vw auto, 29vw auto;
  }
}

@media (max-width: 992px) {

}
@media (max-width: 768px) {
  .welcome-box-bg{
    background:url(../images/wel_bg.png) no-repeat right -3vw top -3vw,
    url(../images/wel_bg.png) no-repeat left 0vw bottom -7vw;
    background-size: 29vw auto, 29vw auto;
  }
}

@media (max-width: 540px) {
   .width {
    width: 95%;
  }
  .middle-menu a {
    width: 33%;
  }
  .middle-menu .middle-menu-item .middle-logo img{
    width: 70%;
  }
  .middle-menu a:nth-child(4){
    margin-top: 10px;
  }
  .welcome-box-bg{
    background:url(../images/wel_bg.png) no-repeat right -10vw top -10vw,
    url(../images/wel_bg.png) no-repeat left 0vw bottom -7vw;
    background-size: 50vw auto, 50vw auto;
  }
    .welcome-title {
        font-size: 20px;
    }
    .welcome-title-cn {
        font-size: 18px;
    }
}

@media (min-width: 768px) {
}

@media (min-width: 992px) {
}

@media (min-width: 1200px) {
}