.image-container {
    background-size: cover;
    background-position: center;
    flex: 1 1 50%;
    width: 100%;
}

.vertical-image-container {
    min-height: 500px;
}

@media ( max-width: 900px ) {
    .image-container: {
        width: 100%;
    }

    .image-container, .vertical-image-container {
        min-height: 250px;
    }
}