My first (more or less) Responsive page

It's the first project using media query for responsive and grid layout for desktop size. I basically didn't have particular problems, i just tried many times positioning all the components and write double the css for the 2 different layout! I'm sure there are many things i can do better, especially the last section with comments (the CSS there is a mess). Any comments and tips will be well accepted, particulary on grid and media query. Everybody happy coding!!