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I'm struggling less with flexbox, but I can't make the footer to get fixed in the bottom, so I used padding to expand the box and throw it down. I guess there's another way to do this but I don't know how.

It was a bit hard to center the main content, I'm not familiar with img width and height. I'm unsure of the @media and I still don't know how many px to set in the width and height. I tried to put <img> into a <div>, but i can't center well, so I let it in the <main>. How can I choose the values of width and height on a img without distortion it?

I don't know how to use media query, i'm not sure how to resize the layout on differents screen sizes.

Is there any difference between id and class in CSS? I don't know who's the best to use.