* {
    box-sizing: border-box;
    padding: 0;
    margin: 0;
}
html, body {
    width: 100%;
    height: 100%;
}
body {
    font-family: Arial, sans-serif;
    background-color: #FFF;
    font-size: 12px;
}

main {
    margin: 10px;
    background-color: #ccc;
}

section {
    display: none;
    padding: 5px;
}