body, html {
    height: 100%;
    margin: 0;
}
.content-wrapper {
    min-height: calc(100vh - 120px); /* header + footer height */
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 2rem;
}
header, footer {
    background-color: #f8f9fa;
    box-shadow: 0 2px 4px rgba(0,0,0,.1);
}
header {
    height: 60px;
}