.container {
    display: flex;
    flex-wrap: wrap;
    padding: 10px;
}

.column {
    flex-basis: 200px;
    padding: 10px;
    box-sizing: border-box;
}

#proizvod {
    background-color: #f0f0f0;
    flex-grow: 1;
}

#kategorija {
    background-color: #e0e0e0;
    flex-grow: 1;
}

#o_nama {
    background-color: #d0d0d0;
    flex-grow: 1;
}

@media (max-width: 768px) {
    .column {
        flex-basis: 100%;
    }
}