Yes I have managed to come out with the same green sale sticker, but I wanted to create an animated one like on the site. I have found the problem in the coding. The pseudo-element is being override by woocommerce span class. As a solution, I just renamed my css class with the same as what woocommerce did in its onsale class. Everything works as I wanted now. Thank you so much for your time, I highly appreciate it.