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.
Currently the max-width property is not changing gradually in Chrome, and does not change at all in Firefox.
CSS Animations are supported in Internet Explorer 10, Firefox, and Opera.
Safari and Chrome supports CSS animations with the prefix -webkit-.