Not only does the grid system split rows horizontally into columns, it also allows you to split the columns vertically, by supporting nested rows. These nested rows themselves are split into 12 columns within the space provided by the parent column. There is nothing special needed in terms of markup to achieve row inception. All that is needed to achieve this is to nest the elements appropriately and apply the row and column classes.
Let's organize our print sizes into the relevant categories. We want 12 size options split equally into four size categories. Each category will contain one row element, with each print size taking up one column in the grid. Let's try the following:
<div class="container"> <h1>Our Print Sizes</h1> <div ...
