"But I don't want to put images in my markup!" Fine, then if you still want to achieve the 100%-fluid width boxes, you need to set the height of the .box to match its width with some simple jQuery. And be sure to fire it whenever you resize the window.
This awesome code ( Responsive Boxes without Images ) is write by Andy McFee, you can se more from this user in the personal repository
You can find the original code on Codepen.io
2018 © Andy McFee