Click the "Try it" button to make sure that the DIV element's width never exceeds 600 pixels:

This DIV element does not have a pre-defined width.

The width of this DIV element is as wide as the parent element allows it to be (100%).

Try resizing the browser window to see that width of this DIV element will grow/shrink along width the resizing.

But if you click the "Try it" button, yo will make sure that this DIV element does not exceed 600 pixels in width.