index.css

/* Note to students: Some properties are given to you to fill out,
others you can modify as they stand, and if you have time,
there are definitely some properties you should add!*/

html {
    height: 100%;
  }
  body {
     background-image: url(light.jpg);
     width: 100%;
     height: 100%;
  }

  header {
      background-color: #8257cb;
      padding: 20px;
      border: 10px solid #000000;
      margin-bottom: 25px; 
      text-align: center;
      font-family: Helvetica
      font-size: 26px;
      display: block;
  }
  nav {
      float: left;
      width: 100%;
  }
  nav ul {
      background-color: #8257cb;
      margin: 0;
      padding: 0;
      width: 10%;
      height: 100%;
      position: fixed;
      float: left;
      border-bottom: ;
      list-style-type: none;
      z-index: 1;
  }
  nav li {
      float: left;
  }
  nav li a {
      display: block;
      height: 25px;
      padding: 12px 18px 8px 18px;
      vertical-align: middle;
  }
  a {
      color: ;
  }
  section {
      text-align: center;
      background-color: gray;
      opacity: .9;
      width: 100%;
      display: inline-block;
      float: inherit;
  }

  footer {
      width: 790px;
      background-color:;
      color:;
      clear: both;
      display: block;
  }

  img {
      
      width: 600px;
  }