Without vertical centering:

    .ex1 {
        MARGIN: AUTO;
        background-color: #005183;
        width: 556px;
        height: 756px;
    }
            
With vertical centering:

    .ex2 {
        TOP: 0;
        BOTTOM: 0;
        LEFT: 0;
        RIGHT: 0;
        MARGIN: AUTO;
        POSITION: ABSOLUTE;
        background-color: #006183;
        width: 556px;
        height: 756px;
    }