.flexcontainerfor2columns {
    display: flex;
    flex-wrap: wrap;
}

.columns1of2 {
    flex: 1;
    padding: 4px;
}
/*
    .columns1of2:nth-child(1) {
        background-color: lightblue;
    }

    .columns1of2:nth-child(2) {
        background-color: lightgreen;
    }*/

@media (max-width: 600px) {
    .columns1of2 {
        flex: 100%;
        max-width: 100%;
    }
}