Responsive component using html and css with media queries

Hey guys, in my last projects I received several feedbacks advising me to make a more semantic html. I did the best I could but I'm still confused when to use <section> and <article> for example. I also tried to use "rem" instead of pixels, but I still have doubts about how it works. And finally, is there any better way to implement the icon overlay?

Thanks for the feedbacks, they help a lot!