#body {
    flex-flow: row wrap;
}

.flex-item {
    align-items: center;
    justify-content: center;
}

.header, .footer {
    flex: 1;
    width: 100%;
    background-color: lightgreen;
}

.main {
    flex: 5;
    height: 60%;
    background-color: lightsalmon;
}

.sidebar {
    flex: 1;
    background-color: lightblue;
}