Mobile first responsive design

This challenge gave me quite the trouble when it comes to javascript haha

When I first started this project it was nearly a month ago, I got tired of javascript and decided to went on a little break reading documentations, books and watch tutorials on javascript, all of it didn't make me understand javascript better, Only after about 21 days I did some codewar problems that I finally understood and grasp how javascript works a little better than before

With the project itself I find that in chrome there is this weird thing where the discount buttons seems to be stretched and I don't know why

Any advice on my project is appreciated, thank you in advance