style.css

body {
    margin: 10px;
    display: flex;
    flex-wrap: wrap;
}

header,
footer,
.full-width {
    flex: 1 100%;
}

section {
    display: flex;
    flex-flow: row wrap;
}

section>h3,
section>h4 {
    margin: 0;
}

section>article {
    flex: 1 100%;
    padding: 10px;
    display: flex;
    align-items: center;
}

section>article>div {
    padding: 10px;
}

section>article>div>form {
    padding: 10px 0;
}

section>#invalidData {
    color: red;
    padding: 10px;
}

section>aside {
    flex: 2 auto;
    padding: 10px;
}

table {
    border-collapse: collapse;
}

table>caption {
    padding: 10px;
}

table>thead>tr>th {
    text-align: left;
    padding: 10px;
}

table>tbody>tr>td {
    padding: 10px;
}

table>thead>tr,
table>tbody>tr {
    border-top: 1px solid #cccccc;
    border-bottom: 1px solid #cccccc;
}