#my_container {
    width: 100%;
    border: 1px solid #000000;
}

#my_container .my_container_row_1 {
    height: 50px;
    background: #FF0000;
}

#my_container .my_container_row_2 {
    height: 50px;
    background: #00FF00;
}

#my_container .my_container_row_3 {
    height: 50px;
    background: #0000FF;
}