Centering Stacked Divs

I’ve created a horizontal row of three <div> that then stack vertically when the screen resizes by using a CSS combination of: width: 33.3333%; min-width: 230px; & float: left;

When the screen resizes, the three <div> continue to float: left.

Is there an easy way through CSS, or some other command native in the theme, that I can use to make the vertically-stacked <div> center align when the screen resizes and they stack?