#my_container {
    position: relative;
    width: 100%;
    height: 400px;
    border: 1px solid #000000;
}

#my_container .box {
    /* WARNING: The parent container should be POSITION: RELATIVE, unless its the HTML Body tag, that's already pos relative */
    position: absolute;
    width: 50px;
    height: 50px;
    border: 2px solid #000000;
}

#my_container .box_1 {
    /* WARNING: left and top wont work correctly without the position set to absolute or fixed */
    left: 0;
    top: 0;
    background: #FF0000;
}

#my_container .box_2 {
    /* WARNING: left and top wont work correctly without the position set to absolute or fixed */
    right: 0;
    top: 0;
    background: #009900;
}

#my_container .box_3 {
    /* WARNING: left and top wont work correctly without the position set to absolute or fixed */
    left: 0;
    bottom: 0;
    background: #009900;
}

#my_container .box_4 {
    /* WARNING: left and top wont work correctly without the position set to absolute or fixed */
    right: 0;
    bottom: 0;
    background: RGBA(255,100,0,0.5)
}