*{box-sizing:border-box;}
  body{
  padding:0;margin:0;
  background:silver;
  font-size:25px;
  }
  header, main, footer, nav {
        width:800px;margin:auto;
        border:5px black;
        }
  header,footer{height:300px;background:green;}
  header{padding-top:60px;}
  .fixed{position:fixed; width:100%;padding:0;z-index:100}
  nav {background:rgb(0,112,255);text-align:center; height:60px; display:flex;
      }
  nav a{display:block;width:25%;line-height:60px;color:blue;}
  nav a:hover{background:rgb(0,160,255);color:white;}
  .active {background:rgb(0,160,255)}
  main{}
  section {padding:10px;}
  section:nth-child(even){background:white;}
  section:nth-child(odd){background:rgb(224,240,255);}  
  h1{padding-top:10px;position:relative;cursor: pointer;}
  h1 div {width:250px; background:red;border-radius:10px;left:20px; top:20px;
          padding:10px;display:none;position:absolute;}
  .panel {display:inline-block;width:285px;height:300px;background:silver;}
  .panel h2 {background:black;color:white;margin:0;}  
  p{text-align:justify;}
  .hide-on-desktop{display:none;}