.absolute {
  position: relative;
}
#intro-wrap {
    position: absolute;
    z-index: 5;
    border-left: 25px solid rgba(0,0,0,.2);
    width: 160px;
    left: -180px;
}
#contentWrap{
    background: #FFFF66;
    padding: 10px;
    height: 800px;
    overflow: auto;
}

    #contentWrap::-webkit-scrollbar {
      width: 12px;
    }

    #contentWrap::-webkit-scrollbar-track {
      -webkit-box-shadow: inset 0 0 6px rgba(173, 173, 173, 0.3);
      border-radius: 10px;
    }

    #contentWrap::-webkit-scrollbar-thumb {
      border-radius: 10px;
      -webkit-box-shadow: inset 0 0 6px rgba(196, 196, 196, 0.5);
    }



#intro-wrap p {
    line-height: 19px;
    color: #999;
}
.open-intro,
.close-intro {
    position:absolute;
    left:160px;
    cursor: pointer;
    width: 85px;
    height: 25px;
    z-index: 50;
    padding-left:15px;
}
.open-intro {
    display: none;
    background: yellow
}
.close-intro {
    background: red;
}

.main-header {
  font-size: 16px;
}