Change the max-width, from "none" to "600px" and back to "none":
This DIV element does not have a pre-defined width.
Try resizing the browser window to see that width of this DIV element will grow/shrink along width the resizing, but it will never exceed 600 pixels in width.
The max-width property is animatable in CSS.
Note: Currently the max-width property is not changing gradually in Chrome, and does not change at all in Firefox.
Note: CSS Animations do not work in Internet Explorer 9 and earlier versions.