* {
  margin: 0;
  padding: 0;
}

.about {
  width: 100%;
  height: 100%;
  overflow: hidden;
}

.about_bgc {
  width: 100%;
}

.about_tit {
  position: absolute;
  top: 280px;
  left: 0;
  right: 0;
  font-size: 28px;
  font-weight: 550;
  bottom: 0;
  width: 800px;
  margin: auto;
  text-align: center;
}

.ribbon {
  display: flex;
  justify-content: center;
  position: absolute;
  right: 30px;
  top: 5px;
  margin: auto;
}

.ribbon:after,
.ribbon:before {
  margin-top: 0.5em;
  content: '';
  display: flex;
  border: 1.5em solid #fff;
}

.ribbon:after {
  border-right-color: transparent;
}

.ribbon:before {
  border-left-color: transparent;
}

.ribbon a:link,
.ribbon a:visited {
  color: #000;
  text-decoration: none;
  height: 3.5em;
  overflow: hidden;
}

.ribbon span {
  background: #fff;
  display: inline-block;
  line-height: 3em;
  padding: 0 1.5em;
  margin-top: 0.5em;
  position: relative;
  -webkit-transition: background-color 0.2s, margin-top 0.2s;
  /* Saf3.2+, Chrome */
  -moz-transition: background-color 0.2s, margin-top 0.2s;
  /* FF4+ */
  -ms-transition: background-color 0.2s, margin-top 0.2s;
  /* IE10 */
  -o-transition: background-color 0.2s, margin-top 0.2s;
  /* Opera 10.5+ */
  transition: background-color 0.2s, margin-top 0.2s;
}

.ribbon a:hover span {
  background: #ffd204;
  margin-top: 0;
}

.ribbon span:before {
  content: '';
  position: absolute;
  top: 3em;
  left: 0;
  border-right: 0.5em solid #9b8651;
  border-bottom: 0.5em solid #fff;
}

.ribbon span:after {
  content: '';
  position: absolute;
  top: 3em;
  right: 0;
  border-left: 0.5em solid #9b8651;
  border-bottom: 0.5em solid #fff;
}

footer {
  /* margin-top: 10px; */
  height: 40px;
  text-align: center;
  line-height: 40px;
  background-color: #ccc;
}
.icon {
  width: 15px;
  height: 15px;
  padding: 5px;
  border: 2px solid #fff;
  border-radius: 100%;
  position: absolute;
  left: 49%;
  bottom: 50px;
  animation: downs 2s linear infinite;
}
/* 返回顶部 */
:root {
  --scroll-Height: 20px; /* 滚动指定距离后，开始展示粘贴元素 */
}

.backer a:not(.backer) {
  width: 200px;
  height: 200px;
  background-color: skyblue;
  display: block;

  position: sticky;

  top: 0; /* 滚动条向上滚动0px后开始粘贴 */
  top: -100px; /* 滚动条向上滚动100px后开始粘贴 */

  /* 向下平移一个视口的高度，隐藏粘贴元素 */
  transform: translateY(calc(100vh));

  /* 向上滚动20px后，粘贴元素出现 */
  transform: translateY(calc(100vh + var(--scroll-Height)));

  /* 向上滚动100px后，粘贴元素被固定，这时是一半的高度露出来 */

  top: -200px; /* 滚动条向上滚动200px后开始粘贴，刚好完全露出粘贴元素 */

  float: right; /* 脱离文档流 + 移动到右边 */
  margin-top: -200px; /* 自身高度， 消除float元素的文字环绕，这时粘贴元素又露出来了 */

  /* 抵消上面的-200px，重新隐藏粘贴元素 */
  transform: translateY(calc(100vh + var(--scroll-Height) + 200px)); /* 向上滚动 scroll-Height + 200 px后，粘贴元素出现 */
  top: calc(-200px - 200px); /* 由于上面的滚动200px后，元素就已经被粘贴固定了，这时元素还不在视口可见范围，这里要加大固定时的阀值 */

  /* 加点间距 */
  margin-right: 20px;
  top: calc(-200px - 200px - var(--scroll-Height) - 20px);
}

/* 实际应用类名 */
.backer {
  width: 40px;
  height: 38px;
  background-color: skyblue;
  border-radius: 50%;
  /* font-size: 32px; */
  display: grid;
  place-items: center;
  position: sticky;
  float: right;
  margin: -200px 25px 0 0;
  transform: translateY(calc(100vh + var(--scroll-Height) + 200px));
  top: calc(-62px - 200px - var(--scroll-Height) - 17px);
  font-size: 12px;
  color: #fff;
  text-decoration: none;
}

.introduce {
  display: flex;
  flex-direction: column;
  background-image: url(../img/beiji.png);
}

.introduce_item {
  display: flex;
  justify-content: center;
  margin-top: 60px;
  margin-bottom: 10px;
}
.introduce_item2 {
  display: flex;
  justify-content: center;
  margin-top: 60px;
  margin-bottom: 10px;
}

.introduce_item_img {
  width: 600px;
  height: 300px;
}

.introduce_item_title {
  width: 300px;
  font-size: 18px;
  line-height: 36px;
  align-self: center;
  padding-left: 100px;
}

.introduce_item_titles {
  width: 300px;
  font-size: 18px;
  line-height: 36px;
  align-self: center;
  padding-right: 100px;
}
@media screen and (max-width: 425px) {
  .about_tit {
    position: absolute;
    top: 88px;
    left: -208px;
    font-size: 16px;
  }
  .ribbon {
    display: flex;
    justify-content: center;
    position: absolute;
    right: 17px;
    top: -8px;
    margin: auto;
  }
  .ribbon span {
    background: #fff;
    display: inline-block;
    line-height: 3em;
    padding: 1px 0.5em;
    margin-top: 0.5em;
    position: relative;
  }
  .ribbon:after,
  .ribbon:before {
    margin-top: 0.5em;
    content: '';
    display: flex;
    border: 0.5em solid #fff;
  }
  .icon {
    width: 15px;
    height: 15px;
    padding: 5px;
    border: 2px solid #fff;
    border-radius: 100%;
    position: absolute;
    left: 47%;
    top: 138px;
  }
  .introduce_item {
    margin-top: 0px;
    display: flex;
    flex-direction: column-reverse;
    align-items: center;
  }
  .introduce_item2 {
    display: flex;
    margin-top: 0px;
    /* margin-bottom: 10px; */
    flex-direction: column;
  }
  .introduce_item_titles {
    /* width: 0; */
    font-size: 16px;
    line-height: 36px;
    align-self: center;
    padding-right: 0;
    text-indent: 2em;
  }

  .introduce_item_title {
    /* width: 300px; */
    font-size: 16px;
    line-height: 36px;
    align-self: center;
    padding-left: 0;
    text-indent: 2em;
  }
  .introduce_item_img {
    /* width: 600px;
    height: 300px; */
    margin-bottom: 10px;
  }
  .backer {
    width: 40px;
    height: 38px;
    background-color: skyblue;
    border-radius: 50%;
    /* font-size: 32px; */
    display: grid;
    place-items: center;
    position: sticky;
    float: right;
    margin: -200px 25px 0 0;
    transform: translateY(calc(100vh + var(--scroll-Height) + 200px));
    top: calc(315px - 200px - var(--scroll-Height) - 17px);
    font-size: 12px;
    color: #fff;
    text-decoration: none;
  }
}