* {
    box-sizing: border-box;
}

html,body {
    margin:0;padding:0;
}

body {
    margin: 0 auto;
    width: 600px;
    font: 15px/1.5 "Helvetica Neue", Helvetica, Arial, sans-serif;
    color: #444;
}

header {
    border-bottom: 3px solid #333;
}

div + div {
    border-top: 1px solid #ccc;
}