Product Preview Card using HTML and CSS

Any general tips for improvement would be really appreciated. This is my first project here and I know the code is a mess so I'm sure there's a lot of room to improve. Also, I started with the desktop version and then worked on the mobile (and was later told that it's best to do the desktop version first)-- when I started working on mobile, the button was the only part of the bottom div (.preview) that was out of the position with part of it outside of the container. I tried to fix it properly but couldn't figure out the root cause so I just added some negative margins on the left side. Any idea why it was leaking out of the container in the first place?