header { background-color: #A9CCE3;
        display: block;
        margin-right: 15%;
        margin-left: 15%;
        text-align: center;
        line-height: normal;

       }
h1 {
     margin-bottom: 0;
   }
h3 {
     margin-bottom: 0;
   }

nav {
      margin-left: 15%;
    }

table, td, tr, th {
       border: 1px solid black;
       }

body {
       margin-left: 10%;
       margin-right: 10%;
     }

footer {
        display: block;
        margin-right: 15%;
        margin-left: 15%;
        text-align: center;
        line-height: normal;
       }