body {
    background-color: aqua;
    background-image: url("../images/background.JPG");
}

header {
    <!-- background-color: gray; -->
}
.container {
    width:960px;
    margin:0 auto;
    <!-- background-color: lightgray; -->
}
.nav_menu{
    list-style:none;
    margin:0;
    padding:0;
}
.nav_menu li {
    min-width: 8em;
    float: left;
    margin-right: 0.5em;
    text-align: center;
}

.nav_menu li a:link,
.nav_menu li a:visited {
    background-color:antiquewhite;
    display:block;
    padding: 0.2em;
    text-decoration: none;
    font-weight: bold;
    margin:0 0 0.2em 0;
    -webkit-border-radius:3px;
    -moz-border-radius:3px;
    border-radius:3px;
    box-shadow: 3px 3px 3px 3px rgba(43,43,77,0.5);
}

.nav_menu a {
    display:block;
    width:90px;
}
.clear {
    clear:both;
}

#mainBody {
    <!-- background-color:gray; -->
}

#welcomeDiv {
    <!-- background-color:grey; -->
}

#leftDiv {
    <!-- background-color:grey; -->
}

#rightDiv {
    <!-- background-color:grey; -->
}