The purpose of the clearfix hack in CSS is to fix a common issue with floated elements.

When an element is floated, it is taken out of the normal document flow. This can cause the parent container to collapse and have zero height.

The clearfix hack provides a way to contain the floated elements within their parent container.

It ensures that the parent container expands to contain the floated elements.

Here's how the clearfix hack works:

1. The parent container is given an overflow property of auto or hidden.

2. After the floated elements inside the container, a pseudo-element (::after) is added.

3. This pseudo-element is also cleared using the clear property.

4. The pseudo-element is then hidden from view using clear:both. By doing this, the parent container recognizes the height of the floated elements. And it expands accordingly to contain them, preventing the collapse issue.

The clearfix hack is a widely used technique in CSS layout. It ensures proper containing of floated elements within their parent containers.