body {
    width: 660px;
    text-align: center;
    margin-left: auto;
    margin-right: auto;
    font-family: ms gothic;
    background-color: #9EBC8A;
    color: #537D5D;
    font-size: 20px;
}
a{
    color: #537D5D;
}
div {
    display: block;
}
#box{
    border: 2px solid #537D5D;
    padding: 5px;
    margin: 5px;
}
.grid-container {
    display: grid;
    grid-template-areas:
        'header header header header'
        'nav main main main'
        'footer footer footer footer'
    ;
}
.header{
    grid-area: header;
}
.main{
    grid-area: main;
}
.nav{
    grid-area: nav;
    text-align: left;
}
.footer{
    grid-area: footer;
}
li{
    list-style:none;
}