Add a custom class to a quilt?

Inactive User not as you describe it (at least to my knowledge), but if you create a custom quilt, for example CategoryPage.landing, then you will get an additional class on the .lia-top-quilt div, e.g. there will be a class like .lia-quilt-category-page-landing

but maybe DougS nows a better way to do that!

Inactive User,

There is no property to define additional class in the quilt.

One way to create new quilt add and assign that to page which will create class as per your new quilt "lia-quilt-layout-two-column-main-side". 

Another way is to add additional class to the element by using JavaScript or Jquery .

Parshant isn't that exactly what I wrote?

Inactive User,  As per luk mentioned in his comment that is the only possibility.

If you are fine to add class during or after page load then use JavaScript.