Applying overflow:auto to the parent (red) div ensures that the floated child divs (col 1, col2 and col3) are contained by it

In the above example the child divs have a min-width:210px set. They are liquid when the browser is above 210px but wont go below 210px when the browser goes small.

If you don't apply the "overflow:auto" property to the red div look what happens:

In the above example the parent red div doesn't enclose the child elements! (And this h4 header is also cramped up against the overflowing child elements)

The child divs will conform to the height and width of the parent div if they have been defined as percentages: