html, body {
    width: 100%;
    height: 100%;
    margin: 0;
    font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  }
  .wrapper {
    width: 100%;
    min-width: 500px;
    justify-content: center;
  }
  
  .logo-wrapper {
    margin: 0 auto 25px auto;
    text-align: center;
  }
  .logo {
    max-height: 90px;
  }
  
  .tags a {
    display: inline-block;
    border: 1px solid gray;
    border-radius: 5px;
    padding: 0 10px;
    color: gray;
    line-height: 24px;
    font-size: 12px;
    text-decoration: none;
    margin: 0 1px;
    margin-bottom: 1px;
  }
  .tags a:hover,
  .tags a:active {
    color: lightblue;
    border-color: lightblue;
    background-color: rgba(255, 255, 255, 0.4);
    text-decoration: none;
  }

  
  .remind_box{
    position: relative;
    display: flex;
    display: inline-block;
    font-size: 32px;
    width: 100%;
    text-align: center;
  }

  .video_box{
    position: relative;
    width: 640px;
    display: flex;
    justify-content: center;
    margin: 0 auto;
  }
  #canvas {
    border-radius: 5px;
    box-shadow: 0 0px 3px rgba(0,0,0,0.12), 0 1px 30px rgba(0,0,0,0.24);
  }
  #video {
    border-radius: 5px;
    box-shadow: 0 0px 3px rgba(0,0,0,0.12), 0 1px 2px rgba(0,0,0,0.24);
    margin: 0 auto;
    position:absolute;
    top: 2px;
    left: 2px;
    width: 10%;
    height: 10%;
    display: flex;
    justify-content: center;
    overflow: hidden;
  }
  .clear{clear:both;}
  
  .box_bottom{
    position: relative;
    width: 640px;
    display: flex;
    justify-content: center;
    margin: 0 auto;
  }
  .tips{
    position: absolute;
    left:0px;
    max-width: 600px;
    margin: 0 auto;
    font-size: 10px;
    color:gray;
    text-align:left;
  }
  
  .feedback {
    position: absolute;
    right: 38px;
    top: 10px;
    max-width: 38px;
    margin: 0 auto;
    text-align:right;
  }
  
  .intro {
    max-width: 640px;
    margin: 0 auto;
    padding: 15px;
  }
  
  
  .intro summary {
    cursor: pointer;
    font-size: 28px;
    color:gray;
    font-weight: bold;
  }
  
  
  .footer {
    display: flex; 
    justify-content: center; 
    align-items: center;
    font-size: 10px;
    text-align:center;
    color: gray;
  }
  
  .footer img {
    width: 60px;
    height: 60px;
    border-radius:10% 10% 10% 10%;
  }