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The overlay part was very hard for me to be able to come up with a code that would work on every device. Like always if there is a better way, feel free to tell me, I'm really curious on this one.

What's the easiest way to get a mobile version of the same webpage? I use @media (max-width: 600px) and put all the modification there, but I don't know if that is the most efficient way of doing it.

The main question that I have is, how to make seamless for smartphones without using a framework, since I'm trying to learn basic HTML and CSS code.