Columns Stacked 2 & 1

By adding stack to the outer div, columns will stack to 2 columns on widths less than 768px and 1 column on widths less than 480px. You can also use this with percentage columns. See also stacking to 1 column.

<div class="f4 stack">
    <div class="one">
        Column 1
    </div>
    <div class="two">
        Column 2
    </div>
    <div class="three">
        Column 3
    </div>
    <div class="four">
        Column 4
    </div>
</div>

Here's the available columns and output:

4 columns

6 columns

8 columns