body {
    font-family: 'Arial', sans-serif;
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

header {
    background-color: #3498db;
    color: #fff;
    text-align: center;
    padding: 1em 0;
}

main {
    display: flex;
    justify-content: space-around;
    flex-wrap: wrap;
    padding: 2em;
}

.app {
    width: 300px;
    margin: 1em;
    padding: 1em;
    border: 1px solid #ccc;
    text-align: center;
}

footer {
    background-color: #3498db;
    color: #fff;
    text-align: center;
    padding: 1em 0;
    position: fixed;
    width: 100%;
    bottom: 0;
}