get size of product from tag li without checkbox when submit add to cart

[eluser]teddy[/eluser]
I have small website sell clothes with size is S, M, XL... and they will be show with tag html li a, I want when user click on it the background li will be change and if user click button 'add to cart' I will get of the size was choosen by user before.

Can I do that if not have checkbox for each size of products?

I attached the picture the size of products showed by other website, it changed background when user click on

Thk for reading topic