body {
display: flex;
flex-flow: row wrap;
margin: 10px auto;
max-width: 40em;
font-family: monospace;
color: #333333;
}

header {
flex: 1 100%;
border: 1px solid;
padding: 10px;
margin: 10px;
background: #f0f0f0;
}

header h1 {
text-align: center;
font-size: 3em;

}