Plz help me out to design a web page that contain DIV'S of different heights and widths whats challenging about this is that i want to design all these DIV'S using a single class

Give them the same class but use ID's for individual divs?

this is a challenging task that not to assign id's nd use a single class

Not sure why you want to do it this way. Seems weird and honestly wrong. If you are forced to do it, and have no way to control the markup, then use nth-child. But in reality use unique ids and classes.