html, body {
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
}

#main {
    width: 50%;
    min-height: 50%;
    margin: auto;
    text-align: center;
    background-color: lightgrey;
    padding: 1em;
    -moz-box-sizing: border-box; -webkit-box-sizing: border-box; box-sizing: border-box;
}

#main h1 {
    margin: 0;
}

table td, th {
    padding: 0.5em;
    border: 1px solid black;
}

table {
    border-collapse: collapse;
    margin: auto;
}