Change the min-width, from "none" to 800px and back to "none":
This DIV element has a pre-defined width: 50%.
An animation will gradually change the min-width to 800 pixels.
The min-width property is animatable in CSS.
Note: The min-width property overrides the width property.
CSS Animations are supported in Internet Explorer 10, Firefox, and Opera.
Safari and Chrome supports CSS animations with the prefix -webkit-.