.BG-img {
  position: fixed;
  top: 0px;
  left: 0px;
  width: 100%;
  height: 100vh;
  z-index: -1;
  -webkit-filter: brightness(78%);
  filter: brightness(78%);
}
.no-bg {
  background: none;
  opacity: 1;
}
.navbar {
  color: #eee;
}
.v-center {
  position: relative;
  top: 16rem;
}
.v-top {
  position: relative;
  top: 16rem;
}

#subtitle,
#subtitle *{
  transition: 1s linear;
}


/* 内容块 */

#board {
  margin: auto;
  background-color: #fff;
  border-radius: 0.5rem;
  z-index: 3;
  -webkit-box-shadow: 0 12px 15px 0 rgba(0, 0, 0, 0.24),
    0 17px 50px 0 rgba(0, 0, 0, 0.19);
  box-shadow: 0 12px 15px 0 rgba(71, 62, 62, 0.24),
    0 17px 50px 0 rgba(0, 0, 0, 0.19);
  position: relative;
  top: 28rem;
}

@media screen and (min-width: 1201px) {
  #board {
    padding: 0 4.2rem 0 4.2rem;
    width: 1080px;
  }
}

@media screen and (max-width: 1200px) {
  #board {
    width: 100%;
    padding: 0 3.5rem 0 3.5rem;
  }
}

@media screen and (max-width: 768px) {
  #board {
    width: 100%;
    padding: 0 1rem 0 1rem;
  }
}

@media screen and (max-width: 420px) {
  #board {
    width: 100%;
    margin: 0 0 0 0;
  }
  .container {
    padding: 0 0 0 0;
  }
}

.position{
  position: relative;
  top: 28rem;;
}

/* 滚动条样式 */
::-webkit-scrollbar {
  width: 4px;
  height: 4px;
  background-color: #f5f5f5;
}
::-webkit-scrollbar-track {
  -webkit-box-shadowinset: 0 0 6px rgba(0, 0, 0, 0.3);
  border-radius: 10px;
  background-color: #f5f5f5;
}
::-webkit-scrollbar-thumb {
  border-radius: 10px;
  -webkit-box-shadow: inset 0 0 6px rgba(0, 0, 0, 0.3);
  background-color: #555;
}

/* 下拉框按钮样式  */
.animated-icon {
    width: 30px;
    height: 20px;
    position: relative;
    margin: 0;
    -webkit-transform: rotate(0deg);
    -moz-transform: rotate(0deg);
    -o-transform: rotate(0deg);
    transform: rotate(0deg);
    -webkit-transition: 0.5s ease-in-out;
    -moz-transition: 0.5s ease-in-out;
    -o-transition: 0.5s ease-in-out;
    transition: 0.5s ease-in-out;
    cursor: pointer;
}

.animated-icon span {
    display: block;
    position: absolute;
    height: 3px;
    width: 100%;
    border-radius: 9px;
    opacity: 1;
    left: 0;
    -webkit-transform: rotate(0deg);
    -moz-transform: rotate(0deg);
    -o-transform: rotate(0deg);
    transform: rotate(0deg);
    -webkit-transition: 0.25s ease-in-out;
    -moz-transition: 0.25s ease-in-out;
    -o-transition: 0.25s ease-in-out;
    transition: 0.25s ease-in-out;
    background: #fff;
}

.animated-icon span:nth-child(1) {
    top: 0;
}

.animated-icon span:nth-child(2) {
    top: 10px;
}

.animated-icon span:nth-child(3) {
    top: 20px;
}