body {
    font-family: sans-serif;
    padding: 2em;
    background: #f4f4f4;
}
section {
    margin-bottom: 2em;
    padding: 1em;
    background: #fff;
    border-left: 4px solid #007acc;
}

.hidden {
    display: none;
}

.highlight {
    background-color: yellow;
}

.alert {
    color: red;
    font-weight: bold;
}