.container {
    border: 1px solid red;
    margin: 10px;
    height: 400px;
    /* justify-content:center; */
    /* align-items: stretch; */
    /* Notice that, the justify-content arranges things across the main axis and the align-items justifies things acrros the cross axis - Also note that main access changes depending on whether we are using flex-direction:  column or flex-direction: row */
}

.item {
    padding: 10px;
    border: 2px solid black;
    margin: 5px;
    text-align: center;
    font-size: xx-large;
    background-color: aquamarine;
}

#rows {
    display: flex;
    flex-direction: row;
}

#columns {
    display: flex;
    flex-direction: column;
}